Commit 4b2e762e authored Jan 19, 2015 by Oleg Nesterov Committed by Borislav Petkov Feb 23, 2015

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>

parent 7aeccb83

arch/x86/kernel/i387.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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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