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Date: Tue, 17 Mar 2015 12:36:58 +0100
From: Quentin Casasnovas <quentin.casasnovas@oracle.com>
To: Borislav Petkov <bp@suse.de>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>,
        Oleg Nesterov <oleg@redhat.com>, Dave Hansen <dave.hansen@intel.com>,
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        Suresh Siddha <sbsiddha@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Yu, Fenghua" <fenghua.yu@intel.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in
 xsave_user/xrestore_user
Message-ID: <20150317113658.GC19131@chrystal.uk.oracle.com>
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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