]> git.ipfire.org Git - thirdparty/kernel/stable.git/commit
x86/cpufeature: Replace the old static_cpu_has() with safe variant
authorBorislav Petkov <bp@suse.de>
Sat, 14 Jul 2018 09:27:01 +0000 (02:27 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 17 Jul 2018 09:31:44 +0000 (11:31 +0200)
commit2d45dae0af88a2602e37e596fdc69f66497f3bb0
tree9efd59da00f13b1a3ebaf0df47cd40f6c24752ef
parent7b2330a33983f103327f929189ef9c8f935d9f0c
x86/cpufeature: Replace the old static_cpu_has() with safe variant

commit bc696ca05f5a8927329ec276a892341e006b00ba upstream

So the old one didn't work properly before alternatives had run.
And it was supposed to provide an optimized JMP because the
assumption was that the offset it is jumping to is within a
signed byte and thus a two-byte JMP.

So I did an x86_64 allyesconfig build and dumped all possible
sites where static_cpu_has() was used. The optimization amounted
to all in all 12(!) places where static_cpu_has() had generated
a 2-byte JMP. Which has saved us a whopping 36 bytes!

This clearly is not worth the trouble so we can remove it. The
only place where the optimization might count - in __switch_to()
- we will handle differently. But that's not subject of this
patch.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1453842730-28463-6-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
Reviewed-by: Matt Helsley (VMware) <matt.helsley@gmail.com>
Reviewed-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Bo Gan <ganb@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
arch/x86/Kconfig.debug
arch/x86/include/asm/cpufeature.h
arch/x86/include/asm/fpu/internal.h
arch/x86/kernel/apic/apic_numachip.c
arch/x86/kernel/cpu/common.c
arch/x86/kernel/vm86_32.c
fs/btrfs/disk-io.c