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Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover from machine checks

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On Fri, Dec 11, 2015 at 2:45 PM, Luck, Tony <tony.luck@intel.com> wrote:
>>> But a machine check safe copy_from_user() would be useful
>>> current generation cpus that broadcast all the time.
>>
>> Fair enough.
>
> Thanks for spending the time to look at this.  Coaxing me to re-write the
> tail of do_machine_check() has made that code much better. Too many
> years of one patch on top of another without looking at the whole context.
>
> Cogitate on this series over the weekend and see if you can give me
> an Acked-by or Reviewed-by (I'll be adding a #define for BIT(63)).

I can't review the MCE decoding part, because I don't understand it
nearly well enough.  The interaction with the core fault handling
looks fine, modulo any need to bikeshed on the macro naming (which
I'll refrain from doing).

I still think it would be better if you get rid of BIT(63) and use a
pair of landing pads, though.  They could be as simple as:

.Lpage_fault_goes_here:
    xorq %rax, %rax
    jmp .Lbad

.Lmce_goes_here:
    /* set high bit of rax or whatever */
    /* fall through */

.Lbad:
    /* deal with it */

That way the magic is isolated to the function that needs the magic.

Also, at least renaming the macro to EXTABLE_MC_PA_IN_AX might be
nice.  It'll keep future users honest.  Maybe some day there'll be a
PA_IN_AX flag, and, heck, maybe some day there'll be ways to get info
for non-MCE faults delivered through fixup_exception.

--Andy
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[PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover from machine checks Tony Luck <tony.luck@intel.com> - 2015-12-11 20:40 +0100
  Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Andy Lutomirski <luto@amacapital.net> - 2015-12-11 21:10 +0100
    RE: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks "Luck, Tony" <tony.luck@intel.com> - 2015-12-11 22:20 +0100
      Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Andy Lutomirski <luto@amacapital.net> - 2015-12-11 23:00 +0100
        RE: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks "Luck, Tony" <tony.luck@intel.com> - 2015-12-11 23:20 +0100
          Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Dan Williams <dan.j.williams@intel.com> - 2015-12-11 23:30 +0100
            Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Andy Lutomirski <luto@amacapital.net> - 2015-12-11 23:30 +0100
              Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Andy Lutomirski <luto@amacapital.net> - 2015-12-11 23:40 +0100
                RE: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks "Luck, Tony" <tony.luck@intel.com> - 2015-12-11 23:50 +0100
                Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Andy Lutomirski <luto@amacapital.net> - 2015-12-12 00:00 +0100
                Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Ingo Molnar <mingo@kernel.org> - 2015-12-14 09:40 +0100
                Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks "Luck, Tony" <tony.luck@intel.com> - 2015-12-14 20:50 +0100
                Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Andy Lutomirski <luto@amacapital.net> - 2015-12-14 21:20 +0100
              RE: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks "Luck, Tony" <tony.luck@intel.com> - 2015-12-11 23:40 +0100
  Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Borislav Petkov <bp@alien8.de> - 2015-12-15 14:20 +0100
    Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Dan Williams <dan.j.williams@intel.com> - 2015-12-15 18:50 +0100
      RE: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks "Luck, Tony" <tony.luck@intel.com> - 2015-12-15 19:00 +0100
        Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Borislav Petkov <bp@alien8.de> - 2015-12-15 19:30 +0100
        Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Dan Williams <dan.j.williams@intel.com> - 2015-12-15 19:30 +0100
          Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Dan Williams <dan.j.williams@intel.com> - 2015-12-15 19:40 +0100
            Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Borislav Petkov <bp@alien8.de> - 2015-12-15 19:40 +0100
              Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Borislav Petkov <bp@alien8.de> - 2015-12-15 20:30 +0100
                RE: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks "Elliott, Robert (Persistent Memory)" <elliott@hpe.com> - 2015-12-15 21:30 +0100
                Re: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks Borislav Petkov <bp@alien8.de> - 2015-12-21 18:40 +0100
              RE: [PATCHV2 3/3] x86, ras: Add mcsafe_memcpy() function to recover  from machine checks "Elliott, Robert (Persistent Memory)" <elliott@hpe.com> - 2015-12-15 20:30 +0100

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