From 4b2e762e2e53c721458a83d547b222178bb72a34 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 19 Jan 2015 19:51:51 +0100 Subject: [PATCH] x86/fpu: Always allow FPU in interrupt if use_eager_fpu() The __thread_has_fpu() check in interrupted_kernel_fpu_idle() was needed to prevent the nested kernel_fpu_begin(). Now that we have in_kernel_fpu and !__thread_has_fpu() case in __kernel_fpu_begin() does not depend on use_eager_fpu() (except clts) we can remove it. __thread_has_fpu() can be false even if use_eager_fpu(), but this case does not differ from !use_eager_fpu() case except we should not worry about X86_CR0_TS, __kernel_fpu_begin()/end() will not touch this bit. Note: I think we can kill all irq_fpu_usable() checks except in_kernel_fpu, just we need to record the state of X86_CR0_TS in __kernel_fpu_begin() and conditionalize stts() in __kernel_fpu_end(), but this needs another patch. Signed-off-by: Oleg Nesterov Reviewed-by: Rik van Riel Acked-by: Andy Lutomirski Cc: Linus Torvalds Cc: Suresh Siddha Link: http://lkml.kernel.org/r/20150119185151.GC16427@redhat.com Signed-off-by: Borislav Petkov --- arch/x86/kernel/i387.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index ad3a2a23f248..8416b5f85806 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -41,8 +41,8 @@ void kernel_fpu_enable(void) * be set (so that the clts/stts pair does nothing that is * visible in the interrupted kernel thread). * - * Except for the eagerfpu case when we return 1 unless we've already - * been eager and saved the state in kernel_fpu_begin(). + * Except for the eagerfpu case when we return true; in the likely case + * the thread has FPU but we are not going to set/clear TS. */ static inline bool interrupted_kernel_fpu_idle(void) { @@ -50,7 +50,7 @@ static inline bool interrupted_kernel_fpu_idle(void) return false; if (use_eager_fpu()) - return __thread_has_fpu(current); + return true; return !__thread_has_fpu(current) && (read_cr0() & X86_CR0_TS);