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Commit 45948d77 authored by Jan Beulich's avatar Jan Beulich Committed by Linus Torvalds
Browse files

[PATCH] x86_64: save FPU context slightly later 



Touching of the floating point state in a kernel debugger must be
NMI-safe, specifically math_state_restore() must be able to deal with
being called out of an NMI context. In order to do that reliably, the
context switch code must take care to not leave a window open where
the current task's TS_USEDFPU flag and CR0.TS could get out of sync.

Signed-off-by: default avatarJan Beulich <jbeulich@novell.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 2b514e74

arch/x86_64/kernel/process.c

+4 −3
Original line number Diff line number Diff line
@@ -527,8 +527,6 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
	int cpu = smp_processor_id();  

	struct tss_struct *tss = &per_cpu(init_tss, cpu);



	unlazy_fpu(prev_p);



	/*

	 * Reload esp0, LDT and the page table pointer:

	 */
@@ -586,11 +584,14 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
	}



	/* 

	 * Switch the PDA context.

	 * Switch the PDA and FPU contexts.

	 */

	prev->userrsp = read_pda(oldrsp); 

	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. */

	unlazy_fpu(prev_p);

	write_pda(kernelstack,

		  task_stack_page(next_p) + THREAD_SIZE - PDA_STACKOFFSET);