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| author |   Borislav Petkov <bp@alien8.de> | 2015-10-09 19:08:59 +0200 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2015-10-11 11:06:40 +0200 |
| commit | 374a3a3916a70fc6236bc2b8f8ac02548a128a54 (patch) | |
| tree | 09a05036d7ed4d73112ce779d01a74bac4dab0f5 /arch/x86/entry | |
| parent | x86/entry: Split and inline syscall_return_slowpath() (diff) | |
| download | linux-dev-374a3a3916a70fc6236bc2b8f8ac02548a128a54.tar.xz linux-dev-374a3a3916a70fc6236bc2b8f8ac02548a128a54.zip | |
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 <bp@suse.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
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/20151009170859.GA24266@pd.tnic
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/entry')
| -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 |