Re: [PATCH 3/8] x86, fpu: kill save_init_fpu(), change math_error() to use unlazy_fpu()

[Rik van Riel]

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On 02/16/2015 04:09 PM, Borislav Petkov wrote:
> On Fri, Feb 06, 2015 at 03:02:00PM -0500, riel@xxxxxxxxxx wrote:
>> From: Oleg Nesterov <oleg@xxxxxxxxxx>

>> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c 
>> index fb4cb6adf225..51c465846f06 100644 ---
>> a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -663,7
>> +663,7 @@ static void math_error(struct pt_regs *regs, int
>> error_code, int trapnr) /* * Save the info for the exception
>> handler and clear the error. */ -	save_init_fpu(task); +
>> unlazy_fpu(task);
> 
> Do I see it correctly that even with this there's a not-so-small
> hole *after* conditional_sti() and *before* unlazy_fpu() where
> caller can still get preempted?

That's ok, the context switch will save the register contents
to memory in that case. At that point unlazy_fpu will potentially
do nothing, and the task will process the FPU context that was
saved to memory previously.

- -- 
All rights reversed
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