From 33a3ebdc077fd85f1bf4d4586eea579b297461ae Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 15 Jan 2015 20:20:05 +0100 Subject: [PATCH] x86, fpu: Don't abuse has_fpu in __kernel_fpu_begin/end() Now that we have in_kernel_fpu we can remove __thread_clear_has_fpu() in __kernel_fpu_begin(). And this allows to replace the asymmetrical and nontrivial use_eager_fpu + tsk_used_math check in kernel_fpu_end() with the same __thread_has_fpu() check. The logic becomes really simple; if _begin() does save() then _end() needs restore(), this is controlled by __thread_has_fpu(). Otherwise they do clts/stts unless use_eager_fpu(). Not only this makes begin/end symmetrical and imo more understandable, potentially this allows to change irq_fpu_usable() to avoid all other checks except "in_kernel_fpu". Also, with this patch __kernel_fpu_end() does restore_fpu_checking() and WARNs if it fails instead of math_state_restore(). I think this looks better because we no longer need __thread_fpu_begin(), and it would be better to report the failure in this case. Signed-off-by: Oleg Nesterov Acked-by: Rik van Riel Cc: matt.fleming@intel.com Cc: bp@suse.de Cc: pbonzini@redhat.com Cc: luto@amacapital.net Cc: Linus Torvalds Cc: Suresh Siddha Link: http://lkml.kernel.org/r/20150115192005.GC27332@redhat.com Signed-off-by: Thomas Gleixner --- arch/x86/kernel/i387.c | 19 ++++++------------- 1 file changed, 6 insertions(+), 13 deletions(-) diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index a81572338243..12088a3f459f 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -81,9 +81,7 @@ void __kernel_fpu_begin(void) this_cpu_write(in_kernel_fpu, true); if (__thread_has_fpu(me)) { - __thread_clear_has_fpu(me); __save_init_fpu(me); - /* We do 'stts()' in __kernel_fpu_end() */ } else if (!use_eager_fpu()) { this_cpu_write(fpu_owner_task, NULL); clts(); @@ -93,17 +91,12 @@ EXPORT_SYMBOL(__kernel_fpu_begin); void __kernel_fpu_end(void) { - if (use_eager_fpu()) { - /* - * For eager fpu, most the time, tsk_used_math() is true. - * Restore the user math as we are done with the kernel usage. - * At few instances during thread exit, signal handling etc, - * tsk_used_math() is false. Those few places will take proper - * actions, so we don't need to restore the math here. - */ - if (likely(tsk_used_math(current))) - math_state_restore(); - } else { + struct task_struct *me = current; + + if (__thread_has_fpu(me)) { + if (WARN_ON(restore_fpu_checking(me))) + drop_init_fpu(me); + } else if (!use_eager_fpu()) { stts(); } -- 2.20.1