Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES

From	Yu-cheng Yu <yu-cheng.yu@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES
Date	2016-04-30 00:50 +0200
Message-ID	<rtpou-5CD-17@gated-at.bofh.it> (permalink)
References	<r92ut-2hO-1@gated-at.bofh.it> <r92uu-2hO-17@gated-at.bofh.it> <rtnd0-3HL-17@gated-at.bofh.it> <rtpeO-5x6-11@gated-at.bofh.it> <rtpeP-5x6-19@gated-at.bofh.it>
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On Fri, Apr 29, 2016 at 03:36:12PM -0700, Dave Hansen wrote:
> On 04/29/2016 03:30 PM, Yu-cheng Yu wrote:
> > On Fri, Apr 29, 2016 at 01:25:34PM -0700, Dave Hansen wrote:
> >> On 03/04/2016 10:12 AM, Yu-cheng Yu wrote:
> >>> +	for (i = 0; i < XFEATURE_MAX; i++) {
> >>> +		/*
> >>> +		 * Copy only in-use xstates.
> >>> +		 */
> >>> +		if (((header.xfeatures >> i) & 1) && xfeature_enabled(i)) {
> >>> +			void *src = get_xsave_addr_no_check(xsave, i);
> >>
> >> How could a bit in header.xfeatures get set if it is not set in
> >> xfeature_enabled() aka xfeatures_mask aka XCR0?
> > 
> > Do you mean, we should test xfeature_enabled(i) first, like,
> > 
> > 	if (xfeature_enabled(i) && ((header.xfeatures >> i) & 1)) ?
> > 
> > The result will be the same, like you said, if XCR0[i] is not set,
> > hader.xfeatures[i] cannot be set.  But if XCR0[i] is set,
> > header.xfeatures[i] can be cleared. 
> 
> I think the xfeature_enabled(i) is probably redundant.  Does it serve
> any actual purpose?

Got it.

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Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES Dave Hansen <dave.hansen@linux.intel.com> - 2016-04-29 22:30 +0200
  Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES Yu-cheng Yu <yu-cheng.yu@intel.com> - 2016-04-30 00:40 +0200
    Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES Dave Hansen <dave.hansen@linux.intel.com> - 2016-04-30 00:40 +0200
      Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES Yu-cheng Yu <yu-cheng.yu@intel.com> - 2016-04-30 00:50 +0200

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