Patch "x86/retpoline: Optimize inline assembler for vmexit_fill_RSB" has been added to the 4.9-stable tree

Patch "x86/retpoline: Optimize inline assembler for vmexit_fill_RSB" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    x86/retpoline: Optimize inline assembler for vmexit_fill_RSB

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-retpoline-optimize-inline-assembler-for-vmexit_fill_rsb.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 3f7d875566d8e79c5e0b2c9a413e91b2c29e0854 Mon Sep 17 00:00:00 2001
From: Andi Kleen <ak@linux.intel.com>
Date: Wed, 17 Jan 2018 14:53:28 -0800
Subject: x86/retpoline: Optimize inline assembler for vmexit_fill_RSB

From: Andi Kleen <ak@linux.intel.com>

commit 3f7d875566d8e79c5e0b2c9a413e91b2c29e0854 upstream.

The generated assembler for the C fill RSB inline asm operations has
several issues:

- The C code sets up the loop register, which is then immediately
  overwritten in __FILL_RETURN_BUFFER with the same value again.

- The C code also passes in the iteration count in another register, which
  is not used at all.

Remove these two unnecessary operations. Just rely on the single constant
passed to the macro for the iterations.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: dave.hansen@intel.com
Cc: gregkh@linuxfoundation.org
Cc: torvalds@linux-foundation.org
Cc: arjan@linux.intel.com
Link: https://lkml.kernel.org/r/20180117225328.15414-1-andi@firstfloor.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/include/asm/nospec-branch.h |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -206,16 +206,17 @@ extern char __indirect_thunk_end[];
 static inline void vmexit_fill_RSB(void)
 {
 #ifdef CONFIG_RETPOLINE
-	unsigned long loops = RSB_CLEAR_LOOPS / 2;
+	unsigned long loops;
 
 	asm volatile (ANNOTATE_NOSPEC_ALTERNATIVE
 		      ALTERNATIVE("jmp 910f",
 				  __stringify(__FILL_RETURN_BUFFER(%0, RSB_CLEAR_LOOPS, %1)),
 				  X86_FEATURE_RETPOLINE)
 		      "910:"
-		      : "=&r" (loops), ASM_CALL_CONSTRAINT
-		      : "r" (loops) : "memory" );
+		      : "=r" (loops), ASM_CALL_CONSTRAINT
+		      : : "memory" );
 #endif
 }
+
 #endif /* __ASSEMBLY__ */
 #endif /* __NOSPEC_BRANCH_H__ */


Patches currently in stable-queue which might be from ak@linux.intel.com are

queue-4.9/perf-tools-fix-build-with-arch-x86_64.patch
queue-4.9/kprobes-x86-disable-optimizing-on-the-function-jumps-to-indirect-thunk.patch
queue-4.9/module-add-retpoline-tag-to-vermagic.patch
queue-4.9/kprobes-x86-blacklist-indirect-thunk-functions-for-kprobes.patch
queue-4.9/x86-retpoline-fill-rsb-on-context-switch-for-affected-cpus.patch
queue-4.9/x86-retpoline-add-lfence-to-the-retpoline-rsb-filling-rsb-macros.patch
queue-4.9/x86-retpoline-optimize-inline-assembler-for-vmexit_fill_rsb.patch
queue-4.9/retpoline-introduce-start-end-markers-of-indirect-thunk.patch