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Commit 0a5ace2a authored by Andi Kleen's avatar Andi Kleen Committed by Andi Kleen
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[PATCH] x86-64: Fix FPU corruption 



This reverts an earlier patch that was found to cause FPU
state corruption. I think the corruption happens because
unlazy_fpu() can cause FPU exceptions and when it happens
after the current switch some processing would affect
the state in the wrong process.

Thanks to  Douglas Crosher and Tom Hughes for testing.

Cc: jbeulich@novell.com

Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent 51ec28e1

arch/x86_64/kernel/process.c

+3 −4
Original line number Diff line number Diff line
@@ -615,6 +615,9 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
		prev->gsindex = gsindex;

	}



	/* Must be after DS reload */

	unlazy_fpu(prev_p);



	/* 

	 * Switch the PDA and FPU contexts.

	 */
@@ -622,10 +625,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
	write_pda(oldrsp, next->userrsp); 

	write_pda(pcurrent, next_p); 



	/* This must be here to ensure both math_state_restore() and

	   kernel_fpu_begin() work consistently. 

	   And the AMD workaround requires it to be after DS reload. */

	unlazy_fpu(prev_p);

	write_pda(kernelstack,

	(unsigned long)task_stack_page(next_p) + THREAD_SIZE - PDA_STACKOFFSET);

#ifdef CONFIG_CC_STACKPROTECTOR