From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: fenghua.yu@intel.com, dvlasenk@redhat.com, peterz@infradead.org,
oleg@redhat.com, mingo@kernel.org, linux-kernel@vger.kernel.org,
brgerst@gmail.com, luto@kernel.org, bp@alien8.de,
jpoimboe@redhat.com, haokexin@gmail.com, hpa@zytor.com,
quentin.casasnovas@oracle.com, tglx@linutronix.de,
torvalds@linux-foundation.org, riel@redhat.com,
linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES area
Date: Mon, 23 Jan 2017 12:57:25 -0800 [thread overview]
Message-ID: <20170123205725.GA3920@test-lenovo> (raw)
In-Reply-To: <2be814b7-9fd6-7955-b4e3-6ecb4ef76052@linux.intel.com>
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
next prev parent reply other threads:[~2017-01-23 21:01 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-22 8:50 [PATCH] x86/fpu: set the xcomp_bv when we fake up a XSAVES area Kevin Hao
2017-01-23 8:28 ` [tip:x86/urgent] x86/fpu: Set " tip-bot for Kevin Hao
2017-01-23 15:36 ` Dave Hansen
2017-01-23 16:55 ` Yu-cheng Yu
2017-01-23 17:23 ` Dave Hansen
2017-01-23 20:57 ` Yu-cheng Yu [this message]
2017-01-23 21:10 ` Dave Hansen
2017-01-23 21:16 ` Yu-cheng Yu
2017-01-23 21:28 ` Dave Hansen
2017-01-24 0:14 ` Kevin Hao
2017-01-24 0:53 ` Dave Hansen
2017-01-24 1:50 ` Kevin Hao
2017-01-24 2:01 ` Dave Hansen
2017-01-24 2:09 ` Kevin Hao
2017-01-24 2:38 ` Dave Hansen
2017-01-24 5:18 ` Kevin Hao
2017-01-24 8:08 ` Ingo Molnar
2017-01-23 9:43 ` tip-bot for Kevin Hao
2017-02-14 16:47 ` Dave Hansen
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