linux-kernel - Re: [RFC PATCH 01/11] x86,fpu: document the data structures a little

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Message-ID: <54B43EDA.2060607@redhat.com>
Date:	Mon, 12 Jan 2015 16:38:34 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Borislav Petkov <bp@...e.de>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	matt.fleming@...el.com, oleg@...hat.com, pbonzini@...hat.com,
	tglx@...utronix.de, luto@...capital.net
Subject: Re: [RFC PATCH 01/11] x86,fpu: document the data structures a little

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On 01/12/2015 04:18 PM, Borislav Petkov wrote:
> On Sun, Jan 11, 2015 at 04:46:23PM -0500, riel@...hat.com wrote:

>> +++ b/arch/x86/include/asm/processor.h @@ -400,6 +400,11 @@
>> struct xsave_struct { /* new processor state extensions will go
>> here */ } __attribute__ ((packed, aligned (64)));
>> 
>> +/* + * The FPU state used depends on the capabilities of the
>> hardware; the + * registers used for vector instructions on newer
>> hardware are included + * in the FPU state. + */ union
>> thread_xstate { struct i387_fsave_struct	fsave; struct
>> i387_fxsave_struct	fxsave; @@ -408,8 +413,8 @@ union
>> thread_xstate { };
>> 
>> struct fpu { -	unsigned int last_cpu; -	unsigned int has_fpu; +
>> unsigned int last_cpu;		/* FPU state last loaded on this CPU */
> 
> Isn't that the last CPU which had the FPU?

Indeed it is. Good catch. I will fix it.

>> +	unsigned int has_fpu;		/* FPU state in current use on CPU */
> 
> I understand ->has_fpu as this thread has the FPU. See comment
> over user_has_fpu().

It does that currently, but the patch to __kernel_fpu_start() changes it
so it can point to a kernel FPU state as well.

- -- 
All rights reversed
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