diff options
| author | Borislav Petkov <[email protected]> | 2015-10-09 19:08:59 +0200 |
|---|---|---|
| committer | Ingo Molnar <[email protected]> | 2015-10-11 11:06:40 +0200 |
| commit | 374a3a3916a70fc6236bc2b8f8ac02548a128a54 (patch) | |
| tree | 09a05036d7ed4d73112ce779d01a74bac4dab0f5 | |
| parent | f5e6a9753ac2965564a14e6285a06f44043ed9c8 (diff) | |
x86/entry/64/compat: Document sysenter_fix_flags's reason for existence
The code under the label can normally be inline, without the
jumping back and forth but the latter is an optimization.
Document that.
Signed-off-by: Borislav Petkov <[email protected]>
Acked-by: Andy Lutomirski <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
| -rw-r--r-- | arch/x86/entry/entry_64_compat.S | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index cf9641cd4796..92b0b27b43c6 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -102,6 +102,12 @@ ENTRY(entry_SYSENTER_compat) * NT was set instead of doing an unconditional popfq. * This needs to happen before enabling interrupts so that * we don't get preempted with NT set. + * + * NB.: sysenter_fix_flags is a label with the code under it moved + * out-of-line as an optimization: NT is unlikely to be set in the + * majority of the cases and instead of polluting the I$ unnecessarily, + * we're keeping that code behind a branch which will predict as + * not-taken and therefore its instructions won't be fetched. */ testl $X86_EFLAGS_NT, EFLAGS(%rsp) jnz sysenter_fix_flags |