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

Oleg Nesterov
2015-03-16T14:59:42Z

On 03/16, Borislav Petkov wrote:
>
> On Sun, Mar 15, 2015 at 05:49:48PM +0100, Oleg Nesterov wrote:
> >
> > And I agree with Quentin, user_insn/check_insn can be improved to allow
> > clobbers, more flexible "output", etc. But imo they already can make this
> > code look a bit better, and "xstate_fault" must die eventually.
>
> FWIW, I did poke at that but there's still something wrong with my macros, will
> take a look when I get a chance:

Sure, I won't argue if we use the new macros instead. But we already have
check_insn/user_insn, why not use them?

For example,

> +#define XSTATE_XSAVE(st, lmask, hmask, err) \
> + asm volatile(ALTERNATIVE_2(XSAVE, \
> + XSAVEOPT, X86_FEATURE_XSAVEOPT, \
> + XSAVES, X86_FEATURE_XSAVES) \
> + "\n" \
> + ".pushsection .fixup,\"ax\"\n" \
> + "3: movl $-1, %[err]\n" \
> + "jmp " alt_end_marker "b\n" \
> + ".popsection\n" \
> + _ASM_EXTABLE(661b, 3b) \
> + : [err] "=r" (err) \
> + : "D" (st), "a" (lmask), "d" (hmask) \
> + : "memory")
> +

to me check_insn(ALTERNATIVE_2(...)) looks better. Except we need the
clobber. It is not easy to read the code like this, imo it would be better
to avoid copy-and-paste and use the helpers we already have. Just we need
to improve them.

But let me repeat, I leave this to you and others, I do not understand
asm enough.

Oleg.