Commit-ID: 374a3a3916a70fc6236bc2b8f8ac02548a128a54 Gitweb: http://git.kernel.org/tip/374a3a3916a70fc6236bc2b8f8ac02548a128a54 Author: Borislav Petkov <[email protected]> AuthorDate: Fri, 9 Oct 2015 19:08:59 +0200 Committer: Ingo Molnar <[email protected]> CommitDate: Sun, 11 Oct 2015 11:06:40 +0200
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]> --- arch/x86/entry/entry_64_compat.S | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index cf9641c..92b0b27 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 -- 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/
