Commit 49200d17 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Borislav Petkov
Browse files

x86/fpu/64: Don't FNINIT in kernel_fpu_begin() 



The remaining callers of kernel_fpu_begin() in 64-bit kernels don't use 387
instructions, so there's no need to sanitize the FPU state.  Skip it to get
most of the performance we lost back.

Reported-by: default avatarKrzysztof Olędzki <ole@ans.pl>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/57f8841ccbf9f3c25a23196c888f5f6ec5887577.1611205691.git.luto@kernel.org
parent b0dc553c

arch/x86/include/asm/fpu/api.h

+12 −0
Original line number Diff line number Diff line
@@ -32,7 +32,19 @@ extern void fpregs_mark_activate(void); 
/* Code that is unaware of kernel_fpu_begin_mask() can use this */

static inline void kernel_fpu_begin(void)

{

#ifdef CONFIG_X86_64

	/*

	 * Any 64-bit code that uses 387 instructions must explicitly request

	 * KFPU_387.

	 */

	kernel_fpu_begin_mask(KFPU_MXCSR);

#else

	/*

	 * 32-bit kernel code may use 387 operations as well as SSE2, etc,

	 * as long as it checks that the CPU has the required capability.

	 */

	kernel_fpu_begin_mask(KFPU_387 | KFPU_MXCSR);

#endif

}



/*