Re: [PATCH -next v6 00/10]arm64: add machine check safe support

[Kefeng Wang]

On 2022/6/21 15:26, Tong Tiangen wrote:
> With the increase of memory capacity and density, the probability of
> memory error increases. The increasing size and density of server RAM
> in the data center and cloud have shown increased uncorrectable memory
> errors.
>
> Currently, the kernel has a mechanism to recover from hardware memory
> errors. This patchset provides an new recovery mechanism.
>
> For arm64, the hardware memory error handling is do_sea() which divided
> into two cases:
>   1. The user state consumed the memory errors, the solution is kill the
>      user process and isolate the error page.
>   2. The kernel state consumed the memory errors, the solution is panic.
>
> For case 2, Undifferentiated panic maybe not the optimal choice, it can be
> handled better, in some scenarios, we can avoid panic, such as uaccess, if the
> uaccess fails due to memory error, only the user process will be affected,
> kill the user process and isolate the user page with hardware memory errors
> is a better choice.
>
> This patchset can be divided into two parts:
>   1. Patch 1~6    - do some restructuring to arm64 extable.
>   2. Patch 7~10   - arm64 add support for machine check safe framework,
>   then ,add two specific scenarios(uaccess/cow) to machine check safe.

It's a good to see more RAS feature on arm64, and we do meet some panic

during copy_from/to_user and CoW processing in our production, for series，

Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>

> Since V5:
>   1. Add patch2/3 to add uaccess assembly helpers.
>   2. Optimize the implementation logic of arm64_do_kernel_sea() in patch8.
>   3. Remove kernel access fixup in patch9.
>   All suggestion are from Mark.
>
> Since V4:
>   1. According Michael's suggestion, add patch5.
>   2. According Mark's suggestiog, do some restructuring to arm64
>   extable, then a new adaptation of machine check safe support is made based
>   on this.
>   3. According Mark's suggestion, support machine check safe in do_mte() in
>   cow scene.
>   4. In V4, two patches have been merged into -next, so V5 not send these
>   two patches.
>
> Since V3:
>   1. According to Robin's suggestion, direct modify user_ldst and
>   user_ldp in asm-uaccess.h and modify mte.S.
>   2. Add new macro USER_MC in asm-uaccess.h, used in copy_from_user.S
>   and copy_to_user.S.
>   3. According to Robin's suggestion, using micro in copy_page_mc.S to
>   simplify code.
>   4. According to KeFeng's suggestion, modify powerpc code in patch1.
>   5. According to KeFeng's suggestion, modify mm/extable.c and some code
>   optimization.
>
> Since V2:
>   1. According to Mark's suggestion, all uaccess can be recovered due to
>      memory error.
>   2. Scenario pagecache reading is also supported as part of uaccess
>      (copy_to_user()) and duplication code problem is also solved.
>      Thanks for Robin's suggestion.
>   3. According Mark's suggestion, update commit message of patch 2/5.
>   4. According Borisllav's suggestion, update commit message of patch 1/5.
>
> Since V1:
>   1.Consistent with PPC/x86, Using CONFIG_ARCH_HAS_COPY_MC instead of
>     ARM64_UCE_KERNEL_RECOVERY.
>   2.Add two new scenes, cow and pagecache reading.
>   3.Fix two small bug(the first two patch).
>
> V1 in here:
> https://lore.kernel.org/lkml/20220323033705.3966643-1-tongtiangen@xxxxxxxxxx/
>
> Tong Tiangen (10):
>    arm64: extable: add new extable type EX_TYPE_KACCESS_ERR_ZERO support
>    arm64: asm-extable: move data fields
>    arm64: asm-extable: add asm uacess helpers
>    arm64: extable: make uaaccess helper use extable type
>      EX_TYPE_UACCESS_ERR_ZERO
>    arm64: extable: move _cond_extable to _cond_uaccess_extable
>    arm64: extable: cleanup redundant extable type EX_TYPE_FIXUP
>    Add generic fallback version of copy_mc_to_user()
>    arm64: add support for machine check error safe
>    arm64: add uaccess to machine check safe
>    arm64: add cow to machine check safe
>
>   arch/arm64/Kconfig                   |  1 +
>   arch/arm64/include/asm/asm-extable.h | 84 ++++++++++++++++++-------
>   arch/arm64/include/asm/asm-uaccess.h | 12 ++--
>   arch/arm64/include/asm/assembler.h   |  8 ++-
>   arch/arm64/include/asm/extable.h     |  1 +
>   arch/arm64/include/asm/mte.h         |  4 ++
>   arch/arm64/include/asm/page.h        | 10 +++
>   arch/arm64/include/asm/uaccess.h     | 94 ++++++++++++++--------------
>   arch/arm64/lib/Makefile              |  2 +
>   arch/arm64/lib/copy_page_mc.S        | 82 ++++++++++++++++++++++++
>   arch/arm64/lib/mte.S                 | 19 ++++++
>   arch/arm64/mm/copypage.c             | 41 +++++++++---
>   arch/arm64/mm/extable.c              | 21 ++++++-
>   arch/arm64/mm/fault.c                | 29 ++++++++-
>   arch/powerpc/include/asm/uaccess.h   |  1 +
>   arch/x86/include/asm/uaccess.h       |  1 +
>   include/linux/highmem.h              |  8 +++
>   include/linux/uaccess.h              |  9 +++
>   mm/memory.c                          |  2 +-
>   19 files changed, 339 insertions(+), 90 deletions(-)
>   create mode 100644 arch/arm64/lib/copy_page_mc.S