Commit-ID: adeb5537849d9db428fe0ddc3562e5a765a347e2 Gitweb: http://git.kernel.org/tip/adeb5537849d9db428fe0ddc3562e5a765a347e2 Author: Denys Vlasenko <[email protected]> AuthorDate: Fri, 15 May 2015 22:39:06 +0200 Committer: Ingo Molnar <[email protected]> CommitDate: Sun, 17 May 2015 07:57:54 +0200
x86/asm/entry/64: Use shorter MOVs from segment registers The "movw %ds,%cx" instruction needs a 0x66 prefix, while "movl %ds,%ecx" does not. The difference is that latter form (on 64-bit CPUs) overwrites the entire %ecx, not only its lower half. But subsequent code doesn't depend on the value of upper half of %ecx, so we can safely use the shorter instruction. The new code is also faster than the old one - now we don't depend on the old value of %ecx, but this code fragment is not performance-critical so it does not matter much. Signed-off-by: Denys Vlasenko <[email protected]> Cc: Alexei Starovoitov <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Frederic Weisbecker <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Kees Cook <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Will Drewry <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/kernel/entry_64.S | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 09c3f9e..47b9581 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1190,17 +1190,17 @@ ENTRY(xen_failsafe_callback) /*CFI_REL_OFFSET ds,DS*/ CFI_REL_OFFSET r11,8 CFI_REL_OFFSET rcx,0 - movw %ds,%cx + movl %ds,%ecx cmpw %cx,0x10(%rsp) CFI_REMEMBER_STATE jne 1f - movw %es,%cx + movl %es,%ecx cmpw %cx,0x18(%rsp) jne 1f - movw %fs,%cx + movl %fs,%ecx cmpw %cx,0x20(%rsp) jne 1f - movw %gs,%cx + movl %gs,%ecx cmpw %cx,0x28(%rsp) jne 1f /* All segments match their saved values => Category 2 (Bad IRET). */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
