From: Jan Beulich Date: Sat, 25 Mar 2006 15:29:25 +0000 (+0100) Subject: [PATCH] x86_64: save FPU context slightly later X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=45948d7720e8bd0104696087c6305fdd90e3b298;p=linux-beck.git [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 Signed-off-by: Andi Kleen Signed-off-by: Linus Torvalds --- 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);