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Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES area

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On Mon, Jan 23, 2017 at 09:23:06AM -0800, Dave Hansen wrote:
> On 01/23/2017 08:55 AM, Yu-cheng Yu wrote:
> >> The best fix here would be not to paper over the issue in the copy
> >> function but find where it got clobbered, or where some initialization
> >> code failed to set it.
> > 
> > Someone else reported different issues from the same bug and a different
> > patch was just tested OK this morning.  I think that adding xfeatures bits
> > to xcomp_bv should have been done in fpstate_init().
> 
> Right.  So where did it get cleared out?

It is not set until a task triggers XSAVES.  We did not set it in fpstate_init()
because there is no valid data at the time.  The problem happens when Linux 
copies data to the XSAVES area, like we see here; the kernel is not expected
to change XSAVES format (xcomp_bv) but xcomp_bv is still blank (except bit 63). 

Because XSAVES format is not changed after boot time and xcomp_bv does not affect
INIT optimization, why don't we fix the problem in fpstate_init()?  

Yu-cheng
 

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[PATCH] x86/fpu: set the xcomp_bv when we fake up a XSAVES area Kevin Hao <haokexin@gmail.com> - 2017-01-22 10:00 +0100
  [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES  area tip-bot for Kevin Hao <tipbot@zytor.com> - 2017-01-23 09:30 +0100
    Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Dave Hansen <dave.hansen@linux.intel.com> - 2017-01-23 16:40 +0100
      Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Yu-cheng Yu <yu-cheng.yu@intel.com> - 2017-01-23 18:00 +0100
        Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Dave Hansen <dave.hansen@linux.intel.com> - 2017-01-23 18:30 +0100
          Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Yu-cheng Yu <yu-cheng.yu@intel.com> - 2017-01-23 22:10 +0100
            Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Dave Hansen <dave.hansen@linux.intel.com> - 2017-01-23 22:20 +0100
              Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Yu-cheng Yu <yu-cheng.yu@intel.com> - 2017-01-23 22:30 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Dave Hansen <dave.hansen@linux.intel.com> - 2017-01-23 22:30 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Kevin Hao <haokexin@gmail.com> - 2017-01-24 01:20 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Dave Hansen <dave.hansen@linux.intel.com> - 2017-01-24 02:00 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Kevin Hao <haokexin@gmail.com> - 2017-01-24 03:00 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Dave Hansen <dave.hansen@linux.intel.com> - 2017-01-24 03:10 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Kevin Hao <haokexin@gmail.com> - 2017-01-24 03:20 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Dave Hansen <dave.hansen@linux.intel.com> - 2017-01-24 03:40 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Kevin Hao <haokexin@gmail.com> - 2017-01-24 06:20 +0100
                Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a  XSAVES area Ingo Molnar <mingo@kernel.org> - 2017-01-24 09:10 +0100
  [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES  area tip-bot for Kevin Hao <tipbot@zytor.com> - 2017-01-23 10:50 +0100

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