wireguard-linux/arch/arc/mm/fault.c, branch jd/unified-crypt-queue

mm: allow VM_FAULT_RETRY for multiple times

2020-04-02T16:35:30Z

The idea comes from a discussion between Linus and Andrea [1]. Before this patch we only allow a page fault to retry once. We achieved this by clearing the FAULT_FLAG_ALLOW_RETRY flag when doing handle_mm_fault() the second time. This was majorly used to avoid unexpected starvation of the system by looping over forever to handle the page fault on a single page. However that should hardly happen, and after all for each code path to return a VM_FAULT_RETRY we'll first wait for a condition (during which time we should possibly yield the cpu) to happen before VM_FAULT_RETRY is really returned. This patch removes the restriction by keeping the FAULT_FLAG_ALLOW_RETRY flag when we receive VM_FAULT_RETRY. It means that the page fault handler now can retry the page fault for multiple times if necessary without the need to generate another page fault event. Meanwhile we still keep the FAULT_FLAG_TRIED flag so page fault handler can still identify whether a page fault is the first attempt or not. Then we'll have these combinations of fault flags (only considering ALLOW_RETRY flag and TRIED flag): - ALLOW_RETRY and !TRIED: this means the page fault allows to retry, and this is the first try - ALLOW_RETRY and TRIED: this means the page fault allows to retry, and this is not the first try - !ALLOW_RETRY and !TRIED: this means the page fault does not allow to retry at all - !ALLOW_RETRY and TRIED: this is forbidden and should never be used In existing code we have multiple places that has taken special care of the first condition above by checking against (fault_flags & FAULT_FLAG_ALLOW_RETRY). This patch introduces a simple helper to detect the first retry of a page fault by checking against both (fault_flags & FAULT_FLAG_ALLOW_RETRY) and !(fault_flag & FAULT_FLAG_TRIED) because now even the 2nd try will have the ALLOW_RETRY set, then use that helper in all existing special paths. One example is in __lock_page_or_retry(), now we'll drop the mmap_sem only in the first attempt of page fault and we'll keep it in follow up retries, so old locking behavior will be retained. This will be a nice enhancement for current code [2] at the same time a supporting material for the future userfaultfd-writeprotect work, since in that work there will always be an explicit userfault writeprotect retry for protected pages, and if that cannot resolve the page fault (e.g., when userfaultfd-writeprotect is used in conjunction with swapped pages) then we'll possibly need a 3rd retry of the page fault. It might also benefit other potential users who will have similar requirement like userfault write-protection. GUP code is not touched yet and will be covered in follow up patch. Please read the thread below for more information. [1] https://lore.kernel.org/lkml/20171102193644.GB22686@redhat.com/ [2] https://lore.kernel.org/lkml/20181230154648.GB9832@redhat.com/ Suggested-by: Linus Torvalds Suggested-by: Andrea Arcangeli Signed-off-by: Peter Xu Signed-off-by: Andrew Morton Tested-by: Brian Geffon Cc: Bobby Powers Cc: David Hildenbrand Cc: Denis Plotnikov Cc: "Dr . David Alan Gilbert" Cc: Hugh Dickins Cc: Jerome Glisse Cc: Johannes Weiner Cc: "Kirill A . Shutemov" Cc: Martin Cracauer Cc: Marty McFadden Cc: Matthew Wilcox Cc: Maya Gokhale Cc: Mel Gorman Cc: Mike Kravetz Cc: Mike Rapoport Cc: Pavel Emelyanov Link: http://lkml.kernel.org/r/20200220160246.9790-1-peterx@redhat.com Signed-off-by: Linus Torvalds

mm: introduce FAULT_FLAG_DEFAULT

2020-04-02T16:35:29Z

Although there're tons of arch-specific page fault handlers, most of them are still sharing the same initial value of the page fault flags. Say, merely all of the page fault handlers would allow the fault to be retried, and they also allow the fault to respond to SIGKILL. Let's define a default value for the fault flags to replace those initial page fault flags that were copied over. With this, it'll be far easier to introduce new fault flag that can be used by all the architectures instead of touching all the archs. Signed-off-by: Peter Xu Signed-off-by: Andrew Morton Tested-by: Brian Geffon Reviewed-by: David Hildenbrand Cc: Andrea Arcangeli Cc: Bobby Powers Cc: Denis Plotnikov Cc: "Dr . David Alan Gilbert" Cc: Hugh Dickins Cc: Jerome Glisse Cc: Johannes Weiner Cc: "Kirill A . Shutemov" Cc: Martin Cracauer Cc: Marty McFadden Cc: Matthew Wilcox Cc: Maya Gokhale Cc: Mel Gorman Cc: Mike Kravetz Cc: Mike Rapoport Cc: Pavel Emelyanov Link: http://lkml.kernel.org/r/20200220160238.9694-1-peterx@redhat.com Signed-off-by: Linus Torvalds

arc/mm: use helper fault_signal_pending()

2020-04-02T16:35:29Z

Let ARC to use the new helper fault_signal_pending() by moving the signal check out of the retry logic as standalone. This should also helps to simplify the code a bit. Signed-off-by: Peter Xu Signed-off-by: Andrew Morton Tested-by: Brian Geffon Cc: Andrea Arcangeli Cc: Bobby Powers Cc: David Hildenbrand Cc: Denis Plotnikov Cc: "Dr . David Alan Gilbert" Cc: Hugh Dickins Cc: Jerome Glisse Cc: Johannes Weiner Cc: "Kirill A . Shutemov" Cc: Martin Cracauer Cc: Marty McFadden Cc: Matthew Wilcox Cc: Maya Gokhale Cc: Mel Gorman Cc: Mike Kravetz Cc: Mike Rapoport Cc: Pavel Emelyanov Link: http://lkml.kernel.org/r/20200220155843.9172-1-peterx@redhat.com Signed-off-by: Linus Torvalds

ARC: mm: remove __ARCH_USE_5LEVEL_HACK

2019-12-01T14:29:19Z

Patch series "elide extraneous generated code for folded p4d/pud/pmd", v3. This series came out of seemingly benign excursion into understanding/removing __ARCH_USE_5LEVEL_HACK from ARC port showing some extraneous code being generated despite folded p4d/pud/pmd | bloat-o-meter2 vmlinux-[AB]* | add/remove: 0/0 grow/shrink: 3/0 up/down: 130/0 (130) | function old new delta | free_pgd_range 548 660 +112 | p4d_clear_bad 2 20 +18 The patches here address that | bloat-o-meter2 vmlinux-[BF]* | add/remove: 0/2 grow/shrink: 0/1 up/down: 0/-386 (-386) | function old new delta | pud_clear_bad 20 - -20 | p4d_clear_bad 20 - -20 | free_pgd_range 660 314 -346 The code savings are not a whole lot, but still worthwhile IMHO. This patch (of 5): With paging code made 5-level compliant, this is no longer needed. ARC has software page walker with 2 lookup levels (pgd -> pte) This was expected to be non functional change but ended with slight code bloat due to needless inclusions of p*d_free_tlb() macros which will be addressed in further patches. | bloat-o-meter2 vmlinux-[AB]* | add/remove: 0/0 grow/shrink: 2/0 up/down: 128/0 (128) | function old new delta | free_pgd_range 546 656 +110 | p4d_clear_bad 2 20 +18 | Total: Before=4137148, After=4137276, chg 0.000000% Link: http://lkml.kernel.org/r/20191016162400.14796-2-vgupta@synopsys.com Signed-off-by: Vineet Gupta Acked-by: Kirill A. Shutemov Cc: "Aneesh Kumar K . V" Cc: Arnd Bergmann Cc: Nick Piggin Cc: Peter Zijlstra Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'arc-5.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc

2019-07-16T22:07:51Z

Pull ARC updates from Vineet Gupta: - long due rewrite of do_page_fault - refactoring of entry/exit code to utilize the double load/store instructions - hsdk platform updates * tag 'arc-5.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc: ARC: [plat-hsdk]: Enable AXI DW DMAC in defconfig ARC: [plat-hsdk]: enable DW SPI controller ARC: hide unused function unw_hdr_alloc ARC: [haps] Add Virtio support ARCv2: entry: simplify return to Delay Slot via interrupt ARC: entry: EV_Trap expects r10 (vs. r9) to have exception cause ARCv2: entry: rewrite to enable use of double load/stores LDD/STD ARCv2: entry: avoid a branch ARCv2: entry: push out the Z flag unclobber from common EXCEPTION_PROLOGUE ARCv2: entry: comments about hardware auto-save on taken interrupts ARC: mm: do_page_fault refactor #8: release mmap_sem sooner ARC: mm: do_page_fault refactor #7: fold the various error handling ARC: mm: do_page_fault refactor #6: error handlers to use same pattern ARC: mm: do_page_fault refactor #5: scoot no_context to end ARC: mm: do_page_fault refactor #4: consolidate retry related logic ARC: mm: do_page_fault refactor #3: tidyup vma access permission code ARC: mm: do_page_fault refactor #2: remove short lived variable ARC: mm: do_page_fault refactor #1: remove label @good_area

Merge branch 'siginfo-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2019-07-09T04:48:15Z

Pull force_sig() argument change from Eric Biederman: "A source of error over the years has been that force_sig has taken a task parameter when it is only safe to use force_sig with the current task. The force_sig function is built for delivering synchronous signals such as SIGSEGV where the userspace application caused a synchronous fault (such as a page fault) and the kernel responded with a signal. Because the name force_sig does not make this clear, and because the force_sig takes a task parameter the function force_sig has been abused for sending other kinds of signals over the years. Slowly those have been fixed when the oopses have been tracked down. This set of changes fixes the remaining abusers of force_sig and carefully rips out the task parameter from force_sig and friends making this kind of error almost impossible in the future" * 'siginfo-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (27 commits) signal/x86: Move tsk inside of CONFIG_MEMORY_FAILURE in do_sigbus signal: Remove the signal number and task parameters from force_sig_info signal: Factor force_sig_info_to_task out of force_sig_info signal: Generate the siginfo in force_sig signal: Move the computation of force into send_signal and correct it. signal: Properly set TRACE_SIGNAL_LOSE_INFO in __send_signal signal: Remove the task parameter from force_sig_fault signal: Use force_sig_fault_to_task for the two calls that don't deliver to current signal: Explicitly call force_sig_fault on current signal/unicore32: Remove tsk parameter from __do_user_fault signal/arm: Remove tsk parameter from __do_user_fault signal/arm: Remove tsk parameter from ptrace_break signal/nds32: Remove tsk parameter from send_sigtrap signal/riscv: Remove tsk parameter from do_trap signal/sh: Remove tsk parameter from force_sig_info_fault signal/um: Remove task parameter from send_sigtrap signal/x86: Remove task parameter from send_sigtrap signal: Remove task parameter from force_sig_mceerr signal: Remove task parameter from force_sig signal: Remove task parameter from force_sigsegv ...

ARC: mm: do_page_fault refactor #8: release mmap_sem sooner

2019-07-01T18:02:22Z

In case of successful page fault handling, this patch releases mmap_sem before updating the perf stat event for major/minor faults. So even though the contention reduction is NOT super high, it is still an improvement. There's an additional code size improvement as we only have 2 up_read() calls now. Note to myself: -------------- 1. Given the way it is done, we are forced to move @bad_area label earlier causing the various "goto bad_area" cases to hit perf stat code. - PERF_COUNT_SW_PAGE_FAULTS is NOW updated for access errors which is what arm/arm64 seem to be doing as well (with slightly different code) - PERF_COUNT_SW_PAGE_FAULTS_{MAJ,MIN} must NOT be updated for the error case which is guarded by now setting @fault initial value to VM_FAULT_ERROR which serves both cases when handle_mm_fault() returns error or is not called at all. 2. arm/arm64 use two homebrew fault flags VM_FAULT_BAD{MAP,MAPACCESS} which I was inclined to add too but seems not needed for ARC - given that we have everything is 1 function we can still use goto - we setup si_code at the right place (arm* do that in the end) - we init fault already to error value which guards entry into perf stats event update Cc: Peter Zijlstra Signed-off-by: Vineet Gupta

ARC: mm: do_page_fault refactor #7: fold the various error handling

2019-07-01T18:02:22Z

- single up_read() call vs. 4 - so much easier on eyes Technically it seems like @bad_area label moved up, but even in old regime, it was a special case of delivering SIGSEGV unconditionally which we now do as well, although with checks. Also note that @fault needs to be initialized since we can land in @bad_area (which reads it) without setting it up with return value of handle_mm_fault() - failing to do so did bite us although as a side effect of different patch: see [1] [1]: http://lists.infradead.org/pipermail/linux-snps-arc/2019-May/005803.html Signed-off-by: Vineet Gupta

ARC: mm: do_page_fault refactor #6: error handlers to use same pattern

2019-07-01T18:02:22Z

- up_read - if !user_mode - whatever error handling Signed-off-by: Vineet Gupta

ARC: mm: do_page_fault refactor #5: scoot no_context to end

2019-07-01T18:02:22Z

This is different than the rest of signal handling stuff No functional change Signed-off-by: Vineet Gupta