[PATCHV4 0/3] Machine check recovery when kernel accesses poison

Tony Luck
2015-12-24T21:09:47Z

Ingo: I think I have fixed up everything to make all the people who
commented happy. Do you have any further suggestions, or is this ready
to go into the tip tree?

This series is initially targeted at the folks doing filesystems
on top of NVDIMMs. They really want to be able to return -EIO
when there is a h/w error (just like spinning rust, and SSD does).

I plan to use the same infrastructure in parts 1&2 to write a
machine check aware "copy_from_user()" that will SIGBUS the
calling application when a syscall touches poison in user space
(just like we do when the application touches the poison itself).

Changes V3-V4:
Andy: Simplify fixup_mcexception() by dropping used-once local variable
Andy: "Reviewed-by" tag added to part1
Boris: Moved new functions to memcpy_64.S and declaration to asm/string_64.h
Boris: Changed name s/mcsafe_memcpy/__mcsafe_copy/ to make it clear that this
is an internal function and that return value doesn't follow memcpy() semantics.
Boris: "Reviewed-by" tag added to parts 1&2

Changes V2-V3:

Andy: Don't hack "regs->ax = BIT(63) | addr;" in the machine check
handler. Now have better fixup code that computes the number
of remaining bytes (just like page-fault fixup).
Andy: #define for BIT(63). Done, plus couple of extra macros using it.
Boris: Don't clutter up generic code (like mm/extable.c) with this.
I moved everything under arch/x86 (the asm-generic change is
a more generic #define).
Boris: Dependencies for CONFIG_MCE_KERNEL_RECOVERY are too generic.
I made it a real menu item with default "n". Dan Williams
will use "select MCE_KERNEL_RECOVERY" from his persistent
filesystem code.
Boris: Simplify conditionals in mce.c by moving tolerant/kill_it
checks earlier, with a skip to end if they aren't set.
Boris: Miscellaneous grammar/punctuation. Fixed.
Boris: Don't leak spurious __start_mcextable symbols into kernels
that didn't configure MCE_KERNEL_RECOVERY. Done.
Tony: New code doesn't belong in user_copy_64.S/uaccess*.h. Moved
to new .S/.h files
Elliott:Cacheing behavior non-optimal. Could use movntdqa, vmovntdqa
or vmovntdqa on source addresses. I didn't fix this yet. Think
of the current mcsafe_memcpy() as the first of several functions.
This one is useful for small copies (meta-data) where the overhead
of saving SSE/AVX state isn't justified.

Changes V1->V2:

0-day: Reported build errors and warnings on 32-bit systems. Fixed
0-day: Reported bloat to tinyconfig. Fixed
Boris: Suggestions to use extra macros to reduce code duplication in _ASM_*EXTABLE. Done
Boris: Re-write "tolerant==3" check to reduce indentation level. See below.
Andy: Check IP is valid before searching kernel exception tables. Done.
Andy: Explain use of BIT(63) on return value from mcsafe_memcpy(). Done (added decode macros).
Andy: Untangle mess of code in tail of do_machine_check() to make it
clear what is going on (e.g. that we only enter the ist_begin_non_atomic()
if we were called from user code, not from kernel!). Done.

Tony Luck (3):
x86, ras: Add new infrastructure for machine check fixup tables
x86, ras: Extend machine check recovery code to annotated ring0 areas
x86, ras: Add __mcsafe_copy() function to recover from machine checks

arch/x86/Kconfig | 10 +++
arch/x86/include/asm/asm.h | 10 ++-
arch/x86/include/asm/mce.h | 14 ++++
arch/x86/include/asm/string_64.h | 8 ++
arch/x86/kernel/cpu/mcheck/mce-severity.c | 21 ++++-
arch/x86/kernel/cpu/mcheck/mce.c | 86 +++++++++++--------
arch/x86/kernel/vmlinux.lds.S | 6 +-
arch/x86/kernel/x8664_ksyms_64.c | 4 +
arch/x86/lib/memcpy_64.S | 133 ++++++++++++++++++++++++++++++
arch/x86/mm/extable.c | 16 ++++
include/asm-generic/vmlinux.lds.h | 12 +--
11 files changed, 276 insertions(+), 44 deletions(-)

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2.1.4