Messages in this thread Patch in this message | | | From | Andy Lutomirski <> | Subject | [PATCH v2 4/4] x86/fpu/64: Don't FNINIT in kernel_fpu_begin() | Date | Tue, 19 Jan 2021 09:39:02 -0800 |
| |
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: Krzysztof Olędzki <ole@ans.pl> Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/x86/include/asm/fpu/api.h | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index 38f4936045ab..435bc59d539b 100644 --- a/arch/x86/include/asm/fpu/api.h +++ b/arch/x86/include/asm/fpu/api.h @@ -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 } /* -- 2.29.2
| |