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| author | Denys Vlasenko | 2015-05-15 22:39:06 +0200 |
|---|---|---|
| committer | Ingo Molnar | 2015-05-17 07:57:54 +0200 |
| commit | adeb5537849d9db428fe0ddc3562e5a765a347e2 (patch) | |
| tree | ec54db194dbab58ffedea8737f9c712cd1abb9f5 | |
| parent | x86/asm/head*.S: Change global labels to local (diff) | |
| download | kernel-qcow2-linux-adeb5537849d9db428fe0ddc3562e5a765a347e2.tar.gz kernel-qcow2-linux-adeb5537849d9db428fe0ddc3562e5a765a347e2.tar.xz kernel-qcow2-linux-adeb5537849d9db428fe0ddc3562e5a765a347e2.zip | |
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 <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1431722346-26585-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 09c3f9e0e07e..47b95813dc37 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). */ |