Messages in this thread Patch in this message | | | Date | Tue, 3 Mar 2015 03:28:00 -0800 | From | tip-bot for Oleg Nesterov <> | Subject | [tip:x86/fpu] x86/fpu: Always allow FPU in interrupt if use_eager_fpu() |
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Commit-ID: 4b2e762e2e53c721458a83d547b222178bb72a34 Gitweb: http://git.kernel.org/tip/4b2e762e2e53c721458a83d547b222178bb72a34 Author: Oleg Nesterov <oleg@redhat.com> AuthorDate: Mon, 19 Jan 2015 19:51:51 +0100 Committer: Borislav Petkov <bp@suse.de> CommitDate: Mon, 23 Feb 2015 15:50:41 +0100
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 <oleg@redhat.com> Reviewed-by: Rik van Riel <riel@redhat.com> Acked-by: Andy Lutomirski <luto@amacapital.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Suresh Siddha <sbsiddha@gmail.com> Link: http://lkml.kernel.org/r/20150119185151.GC16427@redhat.com Signed-off-by: Borislav Petkov <bp@suse.de> --- 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 ad3a2a2..8416b5f 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);
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