Re: [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in xsave_user/xrestore_user

Quentin Casasnovas
2015-03-17T11:35:26Z

On Tue, Mar 17, 2015 at 12:20:15PM +0100, Borislav Petkov wrote:
> On Tue, Mar 17, 2015 at 11:00:46AM +0100, Quentin Casasnovas wrote:
> > Fair point, but AFAIUI we can't do check_insn(XSAVES) alone as of today,
> > and the "..." in your "check_isns(XSAVEOPT, ...)" code above would still
> > need to contain the outputs operands.
>
> I think we can do this (see diff the end of this mail).
>

Right, FWIW I think your approach is valid, but not very generic. Re-using
the check_insn() and making it more generic so we can widen its use felt
like a better approach to me.

AIUI, you didn't like my earlier draft because it wasn't very readable, but
I think this was just due to the (bad) example I took and by reworking it a
bit more, we could end up with the code you previously envisionned:

if (static_cpu_has_safe(X86_FEATURE_XSAVEOPT))
return check_insn(XSAVEOPT, xsave_buf, ...);
else if (static_cpu_has_safe(X86_FEATURE_XSAVES)
return check_insn(XSAVES, xsave_buf, ...);
else
return check_insn(XSAVE, xsave_buf, ...)

Or maybe you were saying the actual macros weren't readable?

> [...]
>
> But including the fault exception table in the macro is already an
> improvement IMO.

Agreed, it already looks much nicer with your diff.

Quentin