x86/fpu: Make the EFI FPU calling convention explicit
EFI uses kernel_fpu_begin() to conform to the UEFI calling convention.
This specifically requires initializing FCW (FPU Control Word), whereas
no sane 64-bit kernel code should use legacy 387 operations that
reference FCW.
This should allow to safely change the default semantics of
kernel_fpu_begin() to stop initializing FCW on 64-bit kernels.
[ bp: Massage commit message a little. ]
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/25d392fff64680e0f4bb8cf0b1003314dc29eafe.1611205691.git.luto@kernel.org
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