From: Borislav Petkov <b...@suse.de>
Date: Fri, 9 Oct 2015 19:04:09 +0200
Subject: [PATCH] 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 <b...@suse.de>
---
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 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
--
2.3.5
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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