linux-kernel - Re: [RFC PATCH 05/11] x86,fpu: ensure FPU state is reloaded from memory if task is traced

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Date:	Tue, 13 Jan 2015 11:57:41 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	matt.fleming@...el.com, bp@...e.de, pbonzini@...hat.com,
	tglx@...utronix.de, luto@...capital.net
Subject: Re: [RFC PATCH 05/11] x86,fpu: ensure FPU state is reloaded from
 memory if task is traced

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On 01/13/2015 11:50 AM, Oleg Nesterov wrote:
> On 01/13, Rik van Riel wrote:
>> 
>>>> @@ -412,8 +412,14 @@ static inline void
>>>> switch_fpu_prepare(struct task_struct *old, struct task_struc
>>>> bool preload = tsk_used_math(new) && (use_eager_fpu() ||
>>>> new->thread.fpu_counter
>>>>> 5); if (__thread_has_fpu(old)) { -		if
>>>>> (!__save_init_fpu(old))
>>>> +		/* +		 * Make sure the FPU state is restored from memory
>>>> next time, +		 * if the task has an FPU exception pending, or
>>>> the task's in +		 * memory FPU state could be changed by a
>>>> debugger. +		 */ +		if (!__save_init_fpu(old) || 
>>>> task_is_stopped_or_traced(old)) cpu = ~0;
>>> 
>>> Well, if debugger wants to change FPU state, it should call 
>>> init_fpu() which resets .last_cpu ?
>> 
>> Does the ptrace (and utrace, and ... ) code actually do that?
> 
> Yes, see xfpregs_get/set. So I think this change is not needed (but
> I didn't look at the next patches).

Excellent, I will drop this then.

- -- 
All rights reversed
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