Re: [patch 01/10] x86/fpu/signal: Clarify exception handling in restore_fpregs_from_user()

[Borislav Petkov]

On Mon, Aug 30, 2021 at 06:27:22PM +0200, Thomas Gleixner wrote:
> FPU restore from a signal frame can trigger various exceptions. The
> exceptions are caught with an exception table entry. The handler of this
> entry sets the error return value to the negated exception number.
> 
> Any other exception than #PF is fatal and recovery is not possible. This
> relies on the fact that the #PF exception number is the same as EFAULT, but
> that's not really obvious.
> 
> Check the error code for -X86_TRAP_PF instead of checking it for -EFAULT to
> make it clear how that works.

I guess you wanna fixup the comment over XSTATE_OP() too and perhaps
mention ex_handler_fault() explicitly so that one can make her/his way
around the code and pinpoint quickly where it sticks that exception
number into rAX.

Thx.

-- 
Regards/Gruss,
    Boris.

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