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

Tony Luck
2015-11-09T18:41:03Z

This is a first draft to show the direction I'm taking to
make it possible for the kernel to recover from machine
checks taken while kernel code is executing.

In a nutshell I'm duplicating the existing annotation mechanism
we use to handle faults when copying to/from user space and
then having the machine check handler check to see if we were
running code in a marked region to fudge the return IP to
point to the recovery path.

Note that I also fudge the return value. I'd like in the future
to be able to write a "mcsafe_copy_from_user()" function that
would be annotated both for page faults, to return a count of
bytes uncopied, or an indication that there was a machine check.
Hence the BIT(63) bit. Internal feedback suggested we'd need
some IS_ERR() like macros to help users decode what happened
to take the right action. But this is "RFC" to see if people
have better ideas on how to handle this.

Almost certainly breaks 32-bit kernels ... while we need to
not break them, I don't see that we need to make this work for
them. Machine check recovery only works on Xeon systems that
have a minimum memory too big for a 32-bit kernel to even boot.

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_memcpy() function to recover from machine checks

arch/x86/include/asm/asm.h | 7 +++
arch/x86/include/asm/uaccess.h | 1 +
arch/x86/include/asm/uaccess_64.h | 3 +
arch/x86/kernel/cpu/mcheck/mce-severity.c | 19 ++++++-
arch/x86/kernel/cpu/mcheck/mce.c | 13 ++++-
arch/x86/kernel/x8664_ksyms_64.c | 2 +
arch/x86/lib/copy_user_64.S | 91 +++++++++++++++++++++++++++++++
arch/x86/mm/extable.c | 16 ++++++
include/asm-generic/vmlinux.lds.h | 6 ++
include/linux/module.h | 1 +
kernel/extable.c | 14 +++++
11 files changed, 168 insertions(+), 5 deletions(-)

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