From: Ingo Molnar Date: Sun, 24 May 2015 07:23:25 +0000 (+0200) Subject: x86/fpu: Micro-optimize the copy_xregs_to_kernel*() and copy_kernel_to_xregs*() functions X-Git-Tag: omap-for-v4.3/legacy-v2-signed~203^2~32 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8c05f05edb7795ecd1fa95d5d44bc5b22fd85287;p=pandora-kernel.git x86/fpu: Micro-optimize the copy_xregs_to_kernel*() and copy_kernel_to_xregs*() functions The copy_xregs_to_kernel*() and copy_kernel_to_xregs*() functions are used to copy FPU registers to kernel memory and vice versa. They are never expected to fail, yet they have a return code, mostly because that way they can share the assembly macros with the copy*user*() functions. This error code is then silently ignored by the context switching and other code - which made the bug in: b8c1b8ea7b21 ("x86/fpu: Fix FPU state save area alignment bug") harder to fix than necessary. So remove the return values and check for no faults when FPU debugging is enabled in the .config. This improves the eagerfpu context switching fast path by a couple of instructions, when FPU debugging is disabled: ffffffff810407fa: 89 c2 mov %eax,%edx ffffffff810407fc: 48 0f ae 2f xrstor64 (%rdi) ffffffff81040800: 31 c0 xor %eax,%eax -ffffffff81040802: eb 0a jmp ffffffff8104080e <__switch_to+0x321> +ffffffff81040802: eb 16 jmp ffffffff8104081a <__switch_to+0x32d> ffffffff81040804: 31 c0 xor %eax,%eax ffffffff81040806: 48 0f ae 8b c0 05 00 fxrstor64 0x5c0(%rbx) ffffffff8104080d: 00 Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed