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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 <ole@ans.pl> Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Borislav Petkov <bp@suse.de> Link: https://lkml.kernel.org/r/57f8841ccbf9f3c25a23196c888f5f6ec5887577.1611205691.git.luto@kernel.org
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@ -32,7 +32,19 @@ extern void fpregs_mark_activate(void);
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/* Code that is unaware of kernel_fpu_begin_mask() can use this */
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static inline void kernel_fpu_begin(void)
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{
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#ifdef CONFIG_X86_64
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/*
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* Any 64-bit code that uses 387 instructions must explicitly request
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* KFPU_387.
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*/
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kernel_fpu_begin_mask(KFPU_MXCSR);
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#else
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/*
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* 32-bit kernel code may use 387 operations as well as SSE2, etc,
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* as long as it checks that the CPU has the required capability.
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*/
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kernel_fpu_begin_mask(KFPU_387 | KFPU_MXCSR);
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#endif
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}
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/*
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