Commit 374a3a39 authored Oct 09, 2015 by Borislav Petkov Committed by Ingo Molnar Oct 11, 2015

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>

parent f5e6a975

arch/x86/entry/entry_64_compat.S

+6 −0

Original line number	Diff line number	Diff line
		@@ -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