linux-dev/Documentation/riscv, branch master

doc: RISC-V: Document that misaligned accesses are supported

2022-10-12T15:58:10Z

The RISC-V ISA manual used to mandate that misaligned accesses were supported in user mode, but that requirement was removed in 2018 via riscv-isa-manual commit 61cadb9 ("Provide new description of misaligned load/store behavior compatible with privileged architecture."). Since the Linux uABI was already frozen at that point it's just been demoted to part of the uABI, but that was never written down. Link: https://lore.kernel.org/r/20220728210715.17214-1-palmer@rivosinc.com Signed-off-by: Palmer Dabbelt

Documentation: riscv: Add sv48 description to VM layout

2022-06-02T03:38:34Z

sv48 was just introduced, so add its virtual memory layout to the documentation. Signed-off-by: Alexandre Ghiti Signed-off-by: Palmer Dabbelt

Documentation: riscv: remove non-existent directory from table of contents

2022-03-31T23:18:56Z

This subdir no longer exists: it was there to document some of the quirks and paths forward for handling them, but those have been dealt with as of Atish's recent patch set. Fixes: 23b1f18326ec ("Documentation: riscv: Remove the old documentation") Link: https://lore.kernel.org/linux-next/20220329133412.591d6882@canb.auug.org.au/ Reported-by: Stephen Rothwell Signed-off-by: Bagas Sanjaya [Palmer: commit text] Signed-off-by: Palmer Dabbelt

Documentation: riscv: Remove the old documentation

2022-03-21T22:01:33Z

The existing pmu documentation describes the limitation of perf infrastructure in RISC-V ISA and limited feature set of perf in RISC-V. However, SBI PMU extension and sscofpmf extension(ISA extension) allows to implement most of the required features of perf. Remove the old documentation which is not accurate anymore. Reviewed-by: Anup Patel Signed-off-by: Atish Patra Signed-off-by: Atish Patra Signed-off-by: Palmer Dabbelt

riscv: Move KASAN mapping next to the kernel mapping

2022-01-20T01:54:04Z

Now that KASAN_SHADOW_OFFSET is defined at compile time as a config, this value must remain constant whatever the size of the virtual address space, which is only possible by pushing this region at the end of the address space next to the kernel mapping. Signed-off-by: Alexandre Ghiti Signed-off-by: Palmer Dabbelt

riscv: Ensure BPF_JIT_REGION_START aligned with PMD size

2021-06-19T04:10:05Z

Andreas reported commit fc8504765ec5 ("riscv: bpf: Avoid breaking W^X") breaks booting with one kind of defconfig, I reproduced a kernel panic with the defconfig: [ 0.138553] Unable to handle kernel paging request at virtual address ffffffff81201220 [ 0.139159] Oops [#1] [ 0.139303] Modules linked in: [ 0.139601] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc5-default+ #1 [ 0.139934] Hardware name: riscv-virtio,qemu (DT) [ 0.140193] epc : __memset+0xc4/0xfc [ 0.140416] ra : skb_flow_dissector_init+0x1e/0x82 [ 0.140609] epc : ffffffff8029806c ra : ffffffff8033be78 sp : ffffffe001647da0 [ 0.140878] gp : ffffffff81134b08 tp : ffffffe001654380 t0 : ffffffff81201158 [ 0.141156] t1 : 0000000000000002 t2 : 0000000000000154 s0 : ffffffe001647dd0 [ 0.141424] s1 : ffffffff80a43250 a0 : ffffffff81201220 a1 : 0000000000000000 [ 0.141654] a2 : 000000000000003c a3 : ffffffff81201258 a4 : 0000000000000064 [ 0.141893] a5 : ffffffff8029806c a6 : 0000000000000040 a7 : ffffffffffffffff [ 0.142126] s2 : ffffffff81201220 s3 : 0000000000000009 s4 : ffffffff81135088 [ 0.142353] s5 : ffffffff81135038 s6 : ffffffff8080ce80 s7 : ffffffff80800438 [ 0.142584] s8 : ffffffff80bc6578 s9 : 0000000000000008 s10: ffffffff806000ac [ 0.142810] s11: 0000000000000000 t3 : fffffffffffffffc t4 : 0000000000000000 [ 0.143042] t5 : 0000000000000155 t6 : 00000000000003ff [ 0.143220] status: 0000000000000120 badaddr: ffffffff81201220 cause: 000000000000000f [ 0.143560] [] __memset+0xc4/0xfc [ 0.143859] [] init_default_flow_dissectors+0x22/0x60 [ 0.144092] [] do_one_initcall+0x3e/0x168 [ 0.144278] [] kernel_init_freeable+0x1c8/0x224 [ 0.144479] [] kernel_init+0x12/0x110 [ 0.144658] [] ret_from_exception+0x0/0xc [ 0.145124] ---[ end trace f1e9643daa46d591 ]--- After some investigation, I think I found the root cause: commit 2bfc6cd81bd ("move kernel mapping outside of linear mapping") moves BPF JIT region after the kernel: | #define BPF_JIT_REGION_START PFN_ALIGN((unsigned long)&_end) The &_end is unlikely aligned with PMD size, so the front bpf jit region sits with part of kernel .data section in one PMD size mapping. But kernel is mapped in PMD SIZE, when bpf_jit_binary_lock_ro() is called to make the first bpf jit prog ROX, we will make part of kernel .data section RO too, so when we write to, for example memset the .data section, MMU will trigger a store page fault. To fix the issue, we need to ensure the BPF JIT region is PMD size aligned. This patch acchieve this goal by restoring the BPF JIT region to original position, I.E the 128MB before kernel .text section. The modification to kasan_init.c is inspired by Alexandre. Fixes: fc8504765ec5 ("riscv: bpf: Avoid breaking W^X") Reported-by: Andreas Schwab Signed-off-by: Jisheng Zhang Signed-off-by: Palmer Dabbelt

Documentation: riscv: Add documentation that describes the VM layout

2021-04-26T15:25:05Z

This new document presents the RISC-V virtual memory layout and is based one the x86 one: it describes the different limits of the different regions of the virtual address space. Signed-off-by: Alexandre Ghiti Signed-off-by: Palmer Dabbelt

docs: archis: add a per-architecture features list

2020-12-03T22:10:15Z

Add a feature list matrix for each architecture to their respective Kernel books. Signed-off-by: Mauro Carvalho Chehab Link: https://lore.kernel.org/r/9c39d4dd93e05c0008205527d2c3450912f029ed.1606748711.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet

Merge tag 'docs-5.6' of git://git.lwn.net/linux

2020-01-29T23:27:31Z

Pull documentation updates from Jonathan Corbet: "It has been a relatively quiet cycle for documentation, but there's still a couple of things of note: - Conversion of the NFS documentation to RST - A new document on how to help with documentation (and a maintainer profile entry too) Plus the usual collection of typo fixes, etc" * tag 'docs-5.6' of git://git.lwn.net/linux: (40 commits) docs: filesystems: add overlayfs to index.rst docs: usb: remove some broken references scripts/find-unused-docs: Fix massive false positives docs: nvdimm: use ReST notation for subsection zram: correct documentation about sysfs node of huge page writeback Documentation: zram: various fixes in zram.rst Add a maintainer entry profile for documentation Add a document on how to contribute to the documentation docs: Keep up with the location of NoUri Documentation: Call out example SYM_FUNC_* usage as x86-specific Documentation: nfs: fault_injection: convert to ReST Documentation: nfs: pnfs-scsi-server: convert to ReST Documentation: nfs: convert pnfs-block-server to ReST Documentation: nfs: idmapper: convert to ReST Documentation: convert nfsd-admin-interfaces to ReST Documentation: nfs-rdma: convert to ReST Documentation: nfsroot.rst: COSMETIC: refill a paragraph Documentation: nfsroot.txt: convert to ReST Documentation: convert nfs.txt to ReST Documentation: filesystems: convert vfat.txt to RST ...

Documentation: riscv: add patch acceptance guidelines

2020-01-05T05:49:01Z

Formalize, in kernel documentation, the patch acceptance policy for arch/riscv. In summary, it states that as maintainers, we plan to only accept patches for new modules or extensions that have been frozen or ratified by the RISC-V Foundation. We've been following these guidelines for the past few months. In the meantime, we've received quite a bit of feedback that it would be helpful to have these guidelines formally documented. Based on a suggestion from Matthew Wilcox, we also add a link to this file to Documentation/process/index.rst, to make this document easier to find. The format of this document has also been changed to align to the format outlined in the maintainer entry profiles, in accordance with comments from Jon Corbet and Dan Williams. Signed-off-by: Paul Walmsley Reviewed-by: Palmer Dabbelt Cc: Palmer Dabbelt Cc: Albert Ou Cc: Krste Asanovic Cc: Andrew Waterman Cc: Matthew Wilcox Cc: Dan Williams Cc: Jonathan Corbet