Patch "pvclock: Add CPU barriers to get correct version value" has been added to the 4.4-stable tree

Patch "pvclock: Add CPU barriers to get correct version value" has been added to the 4.4-stable tree

[gregkh]

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

    pvclock: Add CPU barriers to get correct version value

to the 4.4-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:
     pvclock-add-cpu-barriers-to-get-correct-version-value.patch
and it can be found in the queue-4.4 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 749d088b8e7f4b9826ede02b9a043e417fa84aa1 Mon Sep 17 00:00:00 2001
From: Minfei Huang <mnghuan@gmail.com>
Date: Fri, 27 May 2016 14:17:10 +0800
Subject: pvclock: Add CPU barriers to get correct version value

From: Minfei Huang <mnghuan@gmail.com>

commit 749d088b8e7f4b9826ede02b9a043e417fa84aa1 upstream.

Protocol for the "version" fields is: hypervisor raises it (making it
uneven) before it starts updating the fields and raises it again (making
it even) when it is done.  Thus the guest can make sure the time values
it got are consistent by checking the version before and after reading
them.

Add CPU barries after getting version value just like what function
vread_pvclock does, because all of callees in this function is inline.

Fixes: 502dfeff239e8313bfbe906ca0a1a6827ac8481b
Signed-off-by: Minfei Huang <mnghuan@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/include/asm/pvclock.h |    2 ++
 arch/x86/kernel/pvclock.c      |    4 ++++
 2 files changed, 6 insertions(+)

--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -76,6 +76,8 @@ unsigned __pvclock_read_cycles(const str
 	u8 ret_flags;
 
 	version = src->version;
+	/* Make the latest version visible */
+	smp_rmb();
 
 	offset = pvclock_get_nsec_offset(src);
 	ret = src->system_time + offset;
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -66,6 +66,8 @@ u8 pvclock_read_flags(struct pvclock_vcp
 
 	do {
 		version = __pvclock_read_cycles(src, &ret, &flags);
+		/* Make sure that the version double-check is last. */
+		smp_rmb();
 	} while ((src->version & 1) || version != src->version);
 
 	return flags & valid_flags;
@@ -80,6 +82,8 @@ cycle_t pvclock_clocksource_read(struct
 
 	do {
 		version = __pvclock_read_cycles(src, &ret, &flags);
+		/* Make sure that the version double-check is last. */
+		smp_rmb();
 	} while ((src->version & 1) || version != src->version);
 
 	if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {


Patches currently in stable-queue which might be from mnghuan@gmail.com are

queue-4.4/pvclock-add-cpu-barriers-to-get-correct-version-value.patch