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Userfaultfd is supposed to provide the full address (i.e., unmasked) of
the faulting access back to userspace. However, that is not the case for
quite some time.
Even running "userfaultfd_demo" from the userfaultfd man page provides the
wrong output (and contradicts the man page). Notice that
"UFFD_EVENT_PAGEFAULT event" shows the masked address (7fc5e30b3000) and
not the first read address (0x7fc5e30b300f).
Address returned by mmap() = 0x7fc5e30b3000
fault_handler_thread():
poll() returns: nready = 1; POLLIN = 1; POLLERR = 0
UFFD_EVENT_PAGEFAULT event: flags = 0; address = 7fc5e30b3000
(uffdio_copy.copy returned 4096)
Read address 0x7fc5e30b300f in main(): A
Read address 0x7fc5e30b340f in main(): A
Read address 0x7fc5e30b380f in main(): A
Read address 0x7fc5e30b3c0f in main(): A
The exact address is useful for various reasons and specifically for
prefetching decisions. If it is known that the memory is populated by
certain objects whose size is not page-aligned, then based on the faulting
address, the uffd-monitor can decide whether to prefetch and prefault the
adjacent page.
This bug has been for quite some time in the kernel: since commit
1a29d85eb0f1 ("mm: use vmf->address instead of of vmf->virtual_address")
vmf->virtual_address"), which dates back to 2016. A concern has been
raised that existing userspace application might rely on the old/wrong
behavior in which the address is masked. Therefore, it was suggested to
provide the masked address unless the user explicitly asks for the exact
address.
Add a new userfaultfd feature UFFD_FEATURE_EXACT_ADDRESS to direct
userfaultfd to provide the exact address. Add a new "real_address" field
to vmf to hold the unmasked address. Provide the address to userspace
accordingly.
Initialize real_address in various code-paths to be consistent with
address, even when it is not used, to be on the safe side.
[namit@vmware.com: initialize real_address on all code paths, per Jan]
Link: https://lkml.kernel.org/r/20220226022655.350562-1-namit@vmware.com
[akpm@linux-foundation.org: fix typo in comment, per Jan]
Link: https://lkml.kernel.org/r/20220218041003.3508-1-namit@vmware.com
Signed-off-by: Nadav Amit <namit@vmware.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Now that the feature is fully implemented (the faulting path hooks exist
so userspace is notified, and the ioctl to resolve such faults is
available), advertise this as a supported feature.
Link: https://lkml.kernel.org/r/20210503180737.2487560-6-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Joe Perches <joe@perches.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Wang Qing <wangqing@vivo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This ioctl request reads from uffdio_continue structure written by
userspace which justifies _IOC_WRITE flag. It also writes back to that
structure which justifies _IOC_READ flag.
See NOTEs in include/uapi/asm-generic/ioctl.h for more information.
Fixes: f619147104c8 ("userfaultfd: add UFFDIO_CONTINUE ioctl")
Signed-off-by: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This ioctl is how userspace ought to resolve "minor" userfaults. The
idea is, userspace is notified that a minor fault has occurred. It
might change the contents of the page using its second non-UFFD mapping,
or not. Then, it calls UFFDIO_CONTINUE to tell the kernel "I have
ensured the page contents are correct, carry on setting up the mapping".
Note that it doesn't make much sense to use UFFDIO_{COPY,ZEROPAGE} for
MINOR registered VMAs. ZEROPAGE maps the VMA to the zero page; but in
the minor fault case, we already have some pre-existing underlying page.
Likewise, UFFDIO_COPY isn't useful if we have a second non-UFFD mapping.
We'd just use memcpy() or similar instead.
It turns out hugetlb_mcopy_atomic_pte() already does very close to what
we want, if an existing page is provided via `struct page **pagep`. We
already special-case the behavior a bit for the UFFDIO_ZEROPAGE case, so
just extend that design: add an enum for the three modes of operation,
and make the small adjustments needed for the MCOPY_ATOMIC_CONTINUE
case. (Basically, look up the existing page, and avoid adding the
existing page to the page cache or calling set_page_huge_active() on
it.)
Link: https://lkml.kernel.org/r/20210301222728.176417-5-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Price <steven.price@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Patch series "userfaultfd: add minor fault handling", v9.
Overview
========
This series adds a new userfaultfd feature, UFFD_FEATURE_MINOR_HUGETLBFS.
When enabled (via the UFFDIO_API ioctl), this feature means that any
hugetlbfs VMAs registered with UFFDIO_REGISTER_MODE_MISSING will *also*
get events for "minor" faults. By "minor" fault, I mean the following
situation:
Let there exist two mappings (i.e., VMAs) to the same page(s) (shared
memory). One of the mappings is registered with userfaultfd (in minor
mode), and the other is not. Via the non-UFFD mapping, the underlying
pages have already been allocated & filled with some contents. The UFFD
mapping has not yet been faulted in; when it is touched for the first
time, this results in what I'm calling a "minor" fault. As a concrete
example, when working with hugetlbfs, we have huge_pte_none(), but
find_lock_page() finds an existing page.
We also add a new ioctl to resolve such faults: UFFDIO_CONTINUE. The idea
is, userspace resolves the fault by either a) doing nothing if the
contents are already correct, or b) updating the underlying contents using
the second, non-UFFD mapping (via memcpy/memset or similar, or something
fancier like RDMA, or etc...). In either case, userspace issues
UFFDIO_CONTINUE to tell the kernel "I have ensured the page contents are
correct, carry on setting up the mapping".
Use Case
========
Consider the use case of VM live migration (e.g. under QEMU/KVM):
1. While a VM is still running, we copy the contents of its memory to a
target machine. The pages are populated on the target by writing to the
non-UFFD mapping, using the setup described above. The VM is still running
(and therefore its memory is likely changing), so this may be repeated
several times, until we decide the target is "up to date enough".
2. We pause the VM on the source, and start executing on the target machine.
During this gap, the VM's user(s) will *see* a pause, so it is desirable to
minimize this window.
3. Between the last time any page was copied from the source to the target, and
when the VM was paused, the contents of that page may have changed - and
therefore the copy we have on the target machine is out of date. Although we
can keep track of which pages are out of date, for VMs with large amounts of
memory, it is "slow" to transfer this information to the target machine. We
want to resume execution before such a transfer would complete.
4. So, the guest begins executing on the target machine. The first time it
touches its memory (via the UFFD-registered mapping), userspace wants to
intercept this fault. Userspace checks whether or not the page is up to date,
and if not, copies the updated page from the source machine, via the non-UFFD
mapping. Finally, whether a copy was performed or not, userspace issues a
UFFDIO_CONTINUE ioctl to tell the kernel "I have ensured the page contents
are correct, carry on setting up the mapping".
We don't have to do all of the final updates on-demand. The userfaultfd manager
can, in the background, also copy over updated pages once it receives the map of
which pages are up-to-date or not.
Interaction with Existing APIs
==============================
Because this is a feature, a registered VMA could potentially receive both
missing and minor faults. I spent some time thinking through how the
existing API interacts with the new feature:
UFFDIO_CONTINUE cannot be used to resolve non-minor faults, as it does not
allocate a new page. If UFFDIO_CONTINUE is used on a non-minor fault:
- For non-shared memory or shmem, -EINVAL is returned.
- For hugetlb, -EFAULT is returned.
UFFDIO_COPY and UFFDIO_ZEROPAGE cannot be used to resolve minor faults.
Without modifications, the existing codepath assumes a new page needs to
be allocated. This is okay, since userspace must have a second
non-UFFD-registered mapping anyway, thus there isn't much reason to want
to use these in any case (just memcpy or memset or similar).
- If UFFDIO_COPY is used on a minor fault, -EEXIST is returned.
- If UFFDIO_ZEROPAGE is used on a minor fault, -EEXIST is returned (or -EINVAL
in the case of hugetlb, as UFFDIO_ZEROPAGE is unsupported in any case).
- UFFDIO_WRITEPROTECT simply doesn't work with shared memory, and returns
-ENOENT in that case (regardless of the kind of fault).
Future Work
===========
This series only supports hugetlbfs. I have a second series in flight to
support shmem as well, extending the functionality. This series is more
mature than the shmem support at this point, and the functionality works
fully on hugetlbfs, so this series can be merged first and then shmem
support will follow.
This patch (of 6):
This feature allows userspace to intercept "minor" faults. By "minor"
faults, I mean the following situation:
Let there exist two mappings (i.e., VMAs) to the same page(s). One of the
mappings is registered with userfaultfd (in minor mode), and the other is
not. Via the non-UFFD mapping, the underlying pages have already been
allocated & filled with some contents. The UFFD mapping has not yet been
faulted in; when it is touched for the first time, this results in what
I'm calling a "minor" fault. As a concrete example, when working with
hugetlbfs, we have huge_pte_none(), but find_lock_page() finds an existing
page.
This commit adds the new registration mode, and sets the relevant flag on
the VMAs being registered. In the hugetlb fault path, if we find that we
have huge_pte_none(), but find_lock_page() does indeed find an existing
page, then we have a "minor" fault, and if the VMA has the userfaultfd
registration flag, we call into userfaultfd to handle it.
This is implemented as a new registration mode, instead of an API feature.
This is because the alternative implementation has significant drawbacks
[1].
However, doing it this was requires we allocate a VM_* flag for the new
registration mode. On 32-bit systems, there are no unused bits, so this
feature is only supported on architectures with
CONFIG_ARCH_USES_HIGH_VMA_FLAGS. When attempting to register a VMA in
MINOR mode on 32-bit architectures, we return -EINVAL.
[1] https://lore.kernel.org/patchwork/patch/1380226/
[peterx@redhat.com: fix minor fault page leak]
Link: https://lkml.kernel.org/r/20210322175132.36659-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20210301222728.176417-1-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20210301222728.176417-2-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Patch series "Control over userfaultfd kernel-fault handling", v6.
This patch series is split from [1]. The other series enables SELinux
support for userfaultfd file descriptors so that its creation and movement
can be controlled.
It has been demonstrated on various occasions that suspending kernel code
execution for an arbitrary amount of time at any access to userspace
memory (copy_from_user()/copy_to_user()/...) can be exploited to change
the intended behavior of the kernel. For instance, handling page faults
in kernel-mode using userfaultfd has been exploited in [2, 3]. Likewise,
FUSE, which is similar to userfaultfd in this respect, has been exploited
in [4, 5] for similar outcome.
This small patch series adds a new flag to userfaultfd(2) that allows
callers to give up the ability to handle kernel-mode faults with the
resulting UFFD file object. It then adds a 'user-mode only' option to the
unprivileged_userfaultfd sysctl knob to require unprivileged callers to
use this new flag.
The purpose of this new interface is to decrease the chance of an
unprivileged userfaultfd user taking advantage of userfaultfd to enhance
security vulnerabilities by lengthening the race window in kernel code.
[1] https://lore.kernel.org/lkml/20200211225547.235083-1-dancol@google.com/
[2] https://duasynt.com/blog/linux-kernel-heap-spray
[3] https://duasynt.com/blog/cve-2016-6187-heap-off-by-one-exploit
[4] https://googleprojectzero.blogspot.com/2016/06/exploiting-recursion-in-linux-kernel_20.html
[5] https://bugs.chromium.org/p/project-zero/issues/detail?id=808
This patch (of 2):
userfaultfd handles page faults from both user and kernel code. Add a new
UFFD_USER_MODE_ONLY flag for userfaultfd(2) that makes the resulting
userfaultfd object refuse to handle faults from kernel mode, treating
these faults as if SIGBUS were always raised, causing the kernel code to
fail with EFAULT.
A future patch adds a knob allowing administrators to give some processes
the ability to create userfaultfd file objects only if they pass
UFFD_USER_MODE_ONLY, reducing the likelihood that these processes will
exploit userfaultfd's ability to delay kernel page faults to open timing
windows for future exploits.
Link: https://lkml.kernel.org/r/20201120030411.2690816-1-lokeshgidra@google.com
Link: https://lkml.kernel.org/r/20201120030411.2690816-2-lokeshgidra@google.com
Signed-off-by: Daniel Colascione <dancol@google.com>
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <calin@google.com>
Cc: Daniel Colascione <dancol@dancol.org>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Jeff Vander Stoep <jeffv@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Nitin Gupta <nigupta@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Shaohua Li <shli@fb.com>
Cc: Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Now it's safe to enable write protection in userfaultfd API
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Link: http://lkml.kernel.org/r/20200220163112.11409-15-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Introduce the new uffd-wp APIs for userspace.
Firstly, we'll allow to do UFFDIO_REGISTER with write protection tracking
using the new UFFDIO_REGISTER_MODE_WP flag. Note that this flag can
co-exist with the existing UFFDIO_REGISTER_MODE_MISSING, in which case the
userspace program can not only resolve missing page faults, and at the
same time tracking page data changes along the way.
Secondly, we introduced the new UFFDIO_WRITEPROTECT API to do page level
write protection tracking. Note that we will need to register the memory
region with UFFDIO_REGISTER_MODE_WP before that.
[peterx@redhat.com: write up the commit message]
[peterx@redhat.com: remove useless block, write commit message, check against
VM_MAYWRITE rather than VM_WRITE when register]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20200220163112.11409-14-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This allows UFFDIO_COPY to map pages write-protected.
[peterx@redhat.com: switch to VM_WARN_ON_ONCE in mfill_atomic_pte; add brackets
around "dst_vma->vm_flags & VM_WRITE"; fix wordings in comments and
commit messages]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20200220163112.11409-6-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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|
Many user space API headers are missing licensing information, which
makes it hard for compliance tools to determine the correct license.
By default are files without license information under the default
license of the kernel, which is GPLV2. Marking them GPLV2 would exclude
them from being included in non GPLV2 code, which is obviously not
intended. The user space API headers fall under the syscall exception
which is in the kernels COPYING file:
NOTE! This copyright does *not* cover user programs that use kernel
services by normal system calls - this is merely considered normal use
of the kernel, and does *not* fall under the heading of "derived work".
otherwise syscall usage would not be possible.
Update the files which contain no license information with an SPDX
license identifier. The chosen identifier is 'GPL-2.0 WITH
Linux-syscall-note' which is the officially assigned identifier for the
Linux syscall exception. SPDX license identifiers are a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne. See the previous patch in this series for the
methodology of how this patch was researched.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
|
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No ABI change, but this will make it more explicit to software that ptid
is only available if requested by passing UFFD_FEATURE_THREAD_ID to
UFFDIO_API. The fact it's a union will also self document it shouldn't
be taken for granted there's a tpid there.
Link: http://lkml.kernel.org/r/20170802165145.22628-7-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Alexey Perevalov <a.perevalov@samsung.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
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It could be useful for calculating downtime during postcopy live
migration per vCPU. Side observer or application itself will be
informed about proper task's sleep during userfaultfd processing.
Process's thread id is being provided when user requeste it by setting
UFFD_FEATURE_THREAD_ID bit into uffdio_api.features.
Link: http://lkml.kernel.org/r/20170802165145.22628-6-aarcange@redhat.com
Signed-off-by: Alexey Perevalov <a.perevalov@samsung.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
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In some cases, userfaultfd mechanism should just deliver a SIGBUS signal
to the faulting process, instead of the page-fault event. Dealing with
page-fault event using a monitor thread can be an overhead in these
cases. For example applications like the database could use the
signaling mechanism for robustness purpose.
Database uses hugetlbfs for performance reason. Files on hugetlbfs
filesystem are created and huge pages allocated using fallocate() API.
Pages are deallocated/freed using fallocate() hole punching support.
These files are mmapped and accessed by many processes as shared memory.
The database keeps track of which offsets in the hugetlbfs file have
pages allocated.
Any access to mapped address over holes in the file, which can occur due
to bugs in the application, is considered invalid and expect the process
to simply receive a SIGBUS. However, currently when a hole in the file
is accessed via the mapped address, kernel/mm attempts to automatically
allocate a page at page fault time, resulting in implicitly filling the
hole in the file. This may not be the desired behavior for applications
like the database that want to explicitly manage page allocations of
hugetlbfs files.
Using userfaultfd mechanism with this support to get a signal, database
application can prevent pages from being allocated implicitly when
processes access mapped address over holes in the file.
This patch adds UFFD_FEATURE_SIGBUS feature to userfaultfd mechnism to
request for a SIGBUS signal.
See following for previous discussion about the database requirement
leading to this proposal as suggested by Andrea.
http://www.spinics.net/lists/linux-mm/msg129224.html
Link: http://lkml.kernel.org/r/1501552446-748335-2-git-send-email-prakash.sangappa@oracle.com
Signed-off-by: Prakash Sangappa <prakash.sangappa@oracle.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Patch series "userfaultfd non-cooperative further update for 4.11 merge
window".
Unfortunately I noticed one relevant bug in userfaultfd_exit while doing
more testing. I've been doing testing before and this was also tested
by kbuild bot and exercised by the selftest, but this bug never
reproduced before.
I dropped userfaultfd_exit as result. I dropped it because of
implementation difficulty in receiving signals in __mmput and because I
think -ENOSPC as result from the background UFFDIO_COPY should be enough
already.
Before I decided to remove userfaultfd_exit, I noticed userfaultfd_exit
wasn't exercised by the selftest and when I tried to exercise it, after
moving it to a more correct place in __mmput where it would make more
sense and where the vma list is stable, it resulted in the
event_wait_completion in D state. So then I added the second patch to
be sure even if we call userfaultfd_event_wait_completion too late
during task exit(), we won't risk to generate tasks in D state. The
same check exists in handle_userfault() for the same reason, except it
makes a difference there, while here is just a robustness check and it's
run under WARN_ON_ONCE.
While looking at the userfaultfd_event_wait_completion() function I
looked back at its callers too while at it and I think it's not ok to
stop executing dup_fctx on the fcs list because we relay on
userfaultfd_event_wait_completion to execute
userfaultfd_ctx_put(fctx->orig) which is paired against
userfaultfd_ctx_get(fctx->orig) in dup_userfault just before
list_add(fcs). This change only takes care of fctx->orig but this area
also needs further review looking for similar problems in fctx->new.
The only patch that is urgent is the first because it's an use after
free during a SMP race condition that affects all processes if
CONFIG_USERFAULTFD=y. Very hard to reproduce though and probably
impossible without SLUB poisoning enabled.
This patch (of 3):
I once reproduced this oops with the userfaultfd selftest, it's not
easily reproducible and it requires SLUB poisoning to reproduce.
general protection fault: 0000 [#1] SMP
Modules linked in:
CPU: 2 PID: 18421 Comm: userfaultfd Tainted: G ------------ T 3.10.0+ #15
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.1-0-g8891697-prebuilt.qemu-project.org 04/01/2014
task: ffff8801f83b9440 ti: ffff8801f833c000 task.ti: ffff8801f833c000
RIP: 0010:[<ffffffff81451299>] [<ffffffff81451299>] userfaultfd_exit+0x29/0xa0
RSP: 0018:ffff8801f833fe80 EFLAGS: 00010202
RAX: ffff8801f833ffd8 RBX: 6b6b6b6b6b6b6b6b RCX: ffff8801f83b9440
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8800baf18600
RBP: ffff8801f833fee8 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: ffffffff8127ceb3 R12: 0000000000000000
R13: ffff8800baf186b0 R14: ffff8801f83b99f8 R15: 00007faed746c700
FS: 0000000000000000(0000) GS:ffff88023fc80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007faf0966f028 CR3: 0000000001bc6000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
do_exit+0x297/0xd10
SyS_exit+0x17/0x20
tracesys+0xdd/0xe2
Code: 00 00 66 66 66 66 90 55 48 89 e5 41 54 53 48 83 ec 58 48 8b 1f 48 85 db 75 11 eb 73 66 0f 1f 44 00 00 48 8b 5b 10 48 85 db 74 64 <4c> 8b a3 b8 00 00 00 4d 85 e4 74 eb 41 f6 84 24 2c 01 00 00 80
RIP [<ffffffff81451299>] userfaultfd_exit+0x29/0xa0
RSP <ffff8801f833fe80>
---[ end trace 9fecd6dcb442846a ]---
In the debugger I located the "mm" pointer in the stack and walking
mm->mmap->vm_next through the end shows the vma->vm_next list is fully
consistent and it is null terminated list as expected. So this has to
be an SMP race condition where userfaultfd_exit was running while the
vma list was being modified by another CPU.
When userfaultfd_exit() run one of the ->vm_next pointers pointed to
SLAB_POISON (RBX is the vma pointer and is 0x6b6b..).
The reason is that it's not running in __mmput but while there are still
other threads running and it's not holding the mmap_sem (it can't as it
has to wait the even to be received by the manager). So this is an use
after free that was happening for all processes.
One more implementation problem aside from the race condition:
userfaultfd_exit has really to check a flag in mm->flags before walking
the vma or it's going to slowdown the exit() path for regular tasks.
One more implementation problem: at that point signals can't be
delivered so it would also create a task in D state if the manager
doesn't read the event.
The major design issue: it overall looks superfluous as the manager can
check for -ENOSPC in the background transfer:
if (mmget_not_zero(ctx->mm)) {
[..]
} else {
return -ENOSPC;
}
It's safer to roll it back and re-introduce it later if at all.
[rppt@linux.vnet.ibm.com: documentation fixup after removal of UFFD_EVENT_EXIT]
Link: http://lkml.kernel.org/r/1488345437-4364-1-git-send-email-rppt@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20170224181957.19736-2-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Allow userfaultfd monitor track termination of the processes that have
memory backed by the uffd.
[rppt@linux.vnet.ibm.com: add comment]
Link: http://lkml.kernel.org/r/20170202135448.GB19804@rapoport-lnxLink: http://lkml.kernel.org/r/1485542673-24387-4-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
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When a non-cooperative userfaultfd monitor copies pages in the
background, it may encounter regions that were already unmapped.
Addition of UFFD_EVENT_UNMAP allows the uffd monitor to track precisely
changes in the virtual memory layout.
Since there might be different uffd contexts for the affected VMAs, we
first should create a temporary representation for the unmap event for
each uffd context and then notify them one by one to the appropriate
userfault file descriptors.
The event notification occurs after the mmap_sem has been released.
[arnd@arndb.de: fix nommu build]
Link: http://lkml.kernel.org/r/20170203165141.3665284-1-arnd@arndb.de
[mhocko@suse.com: fix nommu build]
Link: http://lkml.kernel.org/r/20170202091503.GA22823@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/1485542673-24387-3-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Patch series "userfaultfd: non-cooperative: add madvise() event for
MADV_REMOVE request".
These patches add notification of madvise(MADV_REMOVE) event to
non-cooperative userfaultfd monitor.
The first pacth renames EVENT_MADVDONTNEED to EVENT_REMOVE along with
relevant functions and structures. Using _REMOVE instead of
_MADVDONTNEED describes the event semantics more clearly and I hope it's
not too late for such change in the ABI.
This patch (of 3):
The UFFD_EVENT_MADVDONTNEED purpose is to notify uffd monitor about
removal of certain range from address space tracked by userfaultfd.
Hence, UFFD_EVENT_REMOVE seems to better reflect the operation
semantics. Respectively, 'madv_dn' field of uffd_msg is renamed to
'remove' and the madvise_userfault_dontneed callback is renamed to
userfaultfd_remove.
Link: http://lkml.kernel.org/r/1484814154-1557-2-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Userland developers asked to be notified immediately by the UFFDIO_API
ioctl if shmem missing mode is supported by userfaultfd in the running
kernel. This avoids the need to run UFFDIO_REGISTER on a shmem virtual
memory range to find out.
Link: http://lkml.kernel.org/r/20161216144821.5183-38-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Expand the userfaultfd_register/unregister routines to allow shared
memory VMAs.
Currently, there is no UFFDIO_ZEROPAGE and write-protection support for
shared memory VMAs, which is reflected in ioctl methods supported by
uffdio_register.
Link: http://lkml.kernel.org/r/20161216144821.5183-34-aarcange@redhat.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Userland developers asked to be notified immediately by the UFFDIO_API
ioctl if hugetlbfs missing mode is supported by userfaultfd in the
running kernel. This avoids the need to run UFFDIO_REGISTER on a
hugetlbfs virtual memory range to find out.
Link: http://lkml.kernel.org/r/20161216144821.5183-27-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Expand the userfaultfd_register/unregister routines to allow VM_HUGETLB
vmas. huge page alignment checking is performed after a VM_HUGETLB vma
is encountered.
Also, since there is no UFFDIO_ZEROPAGE support for huge pages do not
return that as a valid ioctl method for huge page ranges.
Link: http://lkml.kernel.org/r/20161216144821.5183-22-aarcange@redhat.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
If the page is punched out of the address space the uffd reader should
know this and zeromap the respective area in case of the #PF event.
Link: http://lkml.kernel.org/r/20161216144821.5183-14-aarcange@redhat.com
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
The event denotes that an area [start:end] moves to different location.
Length change isn't reported as "new" addresses, if they appear on the
uffd reader side they will not contain any data and the latter can just
zeromap them.
Waiting for the event ACK is also done outside of mmap sem, as for fork
event.
Link: http://lkml.kernel.org/r/20161216144821.5183-12-aarcange@redhat.com
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
When the mm with uffd-ed vmas fork()-s the respective vmas notify their
uffds with the event which contains a descriptor with new uffd. This
new descriptor can then be used to get events from the child and
populate its mm with data. Note, that there can be different uffd-s
controlling different vmas within one mm, so first we should collect all
those uffds (and ctx-s) in a list and then notify them all one by one
but only once per fork().
The context is created at fork() time but the descriptor, file struct
and anon inode object is created at event read time. So some trickery
is added to the userfaultfd_ctx_read() to handle the ctx queues' locking
vs file creation.
Another thing worth noticing is that the task that fork()-s waits for
the uffd event to get processed WITHOUT the mmap sem.
[aarcange@redhat.com: build warning fix]
Link: http://lkml.kernel.org/r/20161216144821.5183-10-aarcange@redhat.com
Link: http://lkml.kernel.org/r/20161216144821.5183-9-aarcange@redhat.com
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
|
Patch series "userfaultfd tmpfs/hugetlbfs/non-cooperative", v2
These userfaultfd features are finished and are ready for larger
exposure in -mm and upstream merging.
1) tmpfs non present userfault
2) hugetlbfs non present userfault
3) non cooperative userfault for fork/madvise/mremap
qemu development code is already exercising 2) and container postcopy
live migration needs 3).
1) is not currently used but there's a self test and we know some qemu
user for various reasons uses tmpfs as backing for KVM so it'll need it
too to use postcopy live migration with tmpfs memory.
All review feedback from the previous submit has been handled and the
fixes are included. There's no outstanding issue AFIK.
Upstream code just did a s/fe/vmf/ conversion in the page faults and
this has been converted as well incrementally.
In addition to the previous submits, this also wakes up stuck userfaults
during UFFDIO_UNREGISTER. The non cooperative testcase actually
reproduced this problem by getting stuck instead of quitting clean in
some rare case as it could call UFFDIO_UNREGISTER while some userfault
could be still in flight. The other option would have been to keep
leaving it up to userland to serialize itself and to patch the testcase
instead but the wakeup during unregister I think is preferable.
David also asked the UFFD_FEATURE_MISSING_HUGETLBFS and
UFFD_FEATURE_MISSING_SHMEM feature flags to be added so QEMU can avoid
to probe if the hugetlbfs/shmem missing support is available by calling
UFFDIO_REGISTER. QEMU already checks HUGETLBFS_MAGIC with fstatfs so if
UFFD_FEATURE_MISSING_HUGETLBFS is also set, it knows UFFDIO_REGISTER
will succeed (or if it fails, it's for some other more concerning
reason). There's no reason to worry about adding too many feature
flags. There are 64 available and worst case we've to bump the API if
someday we're really going to run out of them.
The round-trip network latency of hugetlbfs userfaults during postcopy
live migration is still of the order of dozen milliseconds on 10GBit if
at 2MB hugepage granularity so it's working perfectly and it should
provide for higher bandwidth or lower CPU usage (which makes it
interesting to add an option in the future to support THP granularity
too for anonymous memory, UFFDIO_COPY would then have to create THP if
alignment/len allows for it). 1GB hugetlbfs granularity will require
big changes in hugetlbfs to work so it's deferred for later.
This patch (of 42):
This adds proper documentation (inline) to avoid the risk of further
misunderstandings about the semantics of _IOW/_IOR and it also reminds
whoever will bump the UFFDIO_API in the future, to change the two ioctl
to _IOW.
This was found while implementing strace support for those ioctl,
otherwise we could have never found it by just reviewing kernel code and
testing it.
_IOC_READ or _IOC_WRITE alters nothing but the ioctl number itself, so
it's only worth fixing if the UFFDIO_API is bumped someday.
Link: http://lkml.kernel.org/r/20161216144821.5183-2-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: "Dmitry V. Levin" <ldv@altlinux.org>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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As include/uapi/linux/userfaultfd.h is a user visible header file, it
should not include kernel-exclusive header files.
So trying to build the userfaultfd test program from the selftests
directory fails, since it contains a reference to linux/compiler.h. As
it turns out, that header is not really needed there, so we can simply
remove it to fix that issue.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This implements the uABI of UFFDIO_COPY and UFFDIO_ZEROPAGE.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Sanidhya Kashyap <sanidhya.gatech@gmail.com>
Cc: zhang.zhanghailiang@huawei.com
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Feiner <pfeiner@google.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Huangpeng (Peter)" <peter.huangpeng@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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I had requests to return the full address (not the page aligned one) to
userland.
It's not entirely clear how the page offset could be relevant because
userfaults aren't like SIGBUS that can sigjump to a different place and it
actually skip resolving the fault depending on a page offset. There's
currently no real way to skip the fault especially because after a
UFFDIO_COPY|ZEROPAGE, the fault is optimized to be retried within the
kernel without having to return to userland first (not even self modifying
code replacing the .text that touched the faulting address would prevent
the fault to be repeated). Userland cannot skip repeating the fault even
more so if the fault was triggered by a KVM secondary page fault or any
get_user_pages or any copy-user inside some syscall which will return to
kernel code. The second time FAULT_FLAG_RETRY_NOWAIT won't be set leading
to a SIGBUS being raised because the userfault can't wait if it cannot
release the mmap_map first (and FAULT_FLAG_RETRY_NOWAIT is required for
that).
Still returning userland a proper structure during the read() on the uffd,
can allow to use the current UFFD_API for the future non-cooperative
extensions too and it looks cleaner as well. Once we get additional
fields there's no point to return the fault address page aligned anymore
to reuse the bits below PAGE_SHIFT.
The only downside is that the read() syscall will read 32bytes instead of
8bytes but that's not going to be measurable overhead.
The total number of new events that can be extended or of new future bits
for already shipped events, is limited to 64 by the features field of the
uffdio_api structure. If more will be needed a bump of UFFD_API will be
required.
[akpm@linux-foundation.org: use __packed]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Sanidhya Kashyap <sanidhya.gatech@gmail.com>
Cc: zhang.zhanghailiang@huawei.com
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Feiner <pfeiner@google.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Huangpeng (Peter)" <peter.huangpeng@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This is (seems to be) the minimal thing that is required to unblock
standard uffd usage from the non-cooperative one. Now more bits can be
added to the features field indicating e.g. UFFD_FEATURE_FORK and others
needed for the latter use-case.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Sanidhya Kashyap <sanidhya.gatech@gmail.com>
Cc: zhang.zhanghailiang@huawei.com
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Feiner <pfeiner@google.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Huangpeng (Peter)" <peter.huangpeng@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Defines the uAPI of the userfaultfd, notably the ioctl numbers and protocol.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Sanidhya Kashyap <sanidhya.gatech@gmail.com>
Cc: zhang.zhanghailiang@huawei.com
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andres Lagar-Cavilla <andreslc@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Feiner <pfeiner@google.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Huangpeng (Peter)" <peter.huangpeng@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
|
Nadav Amit
Axel Rasmussen
Gleb Fotengauer-Malinovskiy
Lokesh Gidra
Shaohua Li
Andrea Arcangeli
Greg Kroah-Hartman
Alexey Perevalov
Prakash Sangappa
Mike Rapoport
Mike Kravetz
Pavel Emelyanov
Andre Przywara