linux-kernel - Re: [tip:x86/urgent] x86/fpu: Set the xcomp

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Date:   Tue, 24 Jan 2017 09:08:10 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Kevin Hao <haokexin@...il.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>, fenghua.yu@...el.com,
        dvlasenk@...hat.com, peterz@...radead.org, oleg@...hat.com,
        linux-kernel@...r.kernel.org, brgerst@...il.com, luto@...nel.org,
        bp@...en8.de, jpoimboe@...hat.com, hpa@...or.com,
        quentin.casasnovas@...cle.com, tglx@...utronix.de,
        torvalds@...ux-foundation.org, riel@...hat.com,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a
 XSAVES area


* Kevin Hao <haokexin@...il.com> wrote:

> > other than helping to hide bugs?
> 
> Why do you think it hide the bug? In contrast, I think my patch fixes what the 
> bug really is. The memory area we fake up is bug, we should fix it there.

The intention is to have a single FPU format set at bootup and xcomp_bv is 
essentially an invariant (constant) inherited by all tasks from early boot. In 
that sense setting xsave.header.xcomp_bv in copyin_to_xsaves() is misplaced.

So I combined the two commits: I kept your original fix but applied Yu-cheng Yu's 
patch that moves the initialization from copyin_to_xsaves() to fpstate_init().

Thanks,

	Ingo