linux-kernel - Re: [patch] x86, avx: don't use avx instructions with "noxsave" boot param

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Message-ID: <50180B2A.6070602@zytor.com>
Date:	Tue, 31 Jul 2012 09:43:22 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	NeilBrown <neilb@...e.de>, james.t.kukunas@...ux.intel.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] x86, avx: don't use avx instructions with "noxsave" boot
 param

On 07/31/2012 09:27 AM, Suresh Siddha wrote:
> On Mon, 2012-07-30 at 21:33 -0700, H. Peter Anvin wrote:
>> I'm wondering if we shouldn't just kill the affected CPUID bits if osxsave is off...
>
> Yes, I considered clearing AVX bit (and any future xsave feature bits)
> as part of the parsing "noxsave" parameter in x86_xsave_setup().
>
> But thought checking for osxsave was more explicit and there are not
> many places using avx code. Also, this follows the SDM guidelines and
> sets a nice precedent for someone (app's) to follow in future.
>
> I am ok either way!
>

My main reason for thinking that it would be good to clear the bits is 
that it plays a lot nicer with alternatives and with static_cpu_has().

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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