From: Glauber Costa <glommer@redhat.com>
Date: Fri, 18 Sep 2009 17:27:23 -0400
Subject: [x86_64] kvm: bound last_kvm to prevent backwards time
Message-id: 1253309243-13769-3-git-send-email-glommer@redhat.com
O-Subject: [PATCH 2/2] RHEL5 BZ524076 try this on on top of the others
Bugzilla: 524076
RH-Acked-by: Rik van Riel <riel@redhat.com>

Since we don't have the whole clocksource infrastructure in place,
we need to make sure that clock don't go backwards. We do this by
checking the value of last_kvm, and using it as a lower bound.

RH-Upstream-status: Specific to RHEL5 port.

Signed-off-by: Glauber Costa <glommer@redhat.com>

diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 90bc1e7..73abf98 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -126,7 +126,11 @@ static inline long do_gettimeoffset_tsc(void)
 
 static inline long do_gettimeoffset_kvm(void)
 {
-	return (kvm_clock_read() - vxtime.last_kvm);
+	unsigned long t;
+	t = kvm_clock_read();
+	if (t < vxtime.last_kvm)
+		t = vxtime.last_kvm;
+	return t -vxtime.last_kvm;
 }
 
 static inline long do_gettimeoffset_hpet(void)