From: Andy Lutomirski Date: Thu, 21 Jan 2021 05:09:51 +0000 (-0800) Subject: x86/fpu/64: Don't FNINIT in kernel_fpu_begin() X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=49200d17d27d5cc1aede2d1bb2a78dbfc1563e65;p=linux.git 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: Krzysztof Olędzki Signed-off-by: Andy Lutomirski Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/57f8841ccbf9f3c25a23196c888f5f6ec5887577.1611205691.git.luto@kernel.org --- diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index 67a4f1cb2aac5..ed33a14188f66 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 } /*