From 45948d7720e8bd0104696087c6305fdd90e3b298 Mon Sep 17 00:00:00 2001 From: Jan Beulich <jbeulich@novell.com> Date: Sat, 25 Mar 2006 16:29:25 +0100 Subject: [PATCH] [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: Jan Beulich <jbeulich@novell.com> Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org> --- arch/x86_64/kernel/process.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c index 0cb93abbf564..81111835722d 100644 --- a/arch/x86_64/kernel/process.c +++ b/arch/x86_64/kernel/process.c @@ -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); -- 2.20.1