linux-kernel - Re: [PATCH 1/3] x86, fpu: decouple non-lazy/eager fpu restore from xsave

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Message-ID: <504A414E.40507@zytor.com>
Date:	Fri, 07 Sep 2012 11:47:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	mingo@...nel.org, torvalds@...ux-foundation.org,
	andreas.herrmann3@....com, bp@...64.org, robert.richter@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] x86, fpu: decouple non-lazy/eager fpu restore from
 xsave

On 09/07/2012 11:31 AM, Suresh Siddha wrote:
>
> +static inline void fx_finit(struct i387_fxsave_struct *fx)
> +{
> +	memset(fx, 0, xstate_size);
> +	fx->cwd = 0x37f;
> +	if (cpu_has_xmm)
> +		fx->mxcsr = MXCSR_DEFAULT;
> +}
> +

Incidentally, Al Viro asked a very good question the other day, which is 
why can't we just set mxcsr unconditionally here?  I don't think any 
CPUs with FXSAVE and no MXCSR (Pentium II from Intel, 
Crusoe/TM-3xxx/5xxx from Transmeta, and presumably some of the K6 
generation from AMD) ever looked at this field.

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

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