| From | riel@redhat ... | Subject | [RFC PATCH 05/11] x86,fpu: ensure FPU state is reloaded from memory if task is traced | Date | Sun, 11 Jan 2015 16:46:27 -0500 |
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From: Rik van Riel <riel@redhat.com>
If the old task is in a state where its FPU state could be changed by a debugger, ensure the FPU state is always restored from memory on the next context switch.
Currently the system only skips FPU reloads when !eager_fpu_mode() and the task's FPU state is still loaded on the CPU.
Signed-off-by: Rik van Riel <riel@redhat.com> --- arch/x86/include/asm/fpu-internal.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h index 539b050..4db8781 100644 --- a/arch/x86/include/asm/fpu-internal.h +++ b/arch/x86/include/asm/fpu-internal.h @@ -412,8 +412,14 @@ static inline void switch_fpu_prepare(struct task_struct *old, struct task_struc bool preload = tsk_used_math(new) && (use_eager_fpu() || new->thread.fpu_counter > 5); if (__thread_has_fpu(old)) { - if (!__save_init_fpu(old)) + /* + * Make sure the FPU state is restored from memory next time, + * if the task has an FPU exception pending, or the task's in + * memory FPU state could be changed by a debugger. + */ + if (!__save_init_fpu(old) || task_is_stopped_or_traced(old)) cpu = ~0; + old->thread.fpu.last_cpu = cpu; old->thread.fpu.has_fpu = 0; /* But leave fpu_owner_task! */ -- 1.9.3
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