x86: don't pass negative time to gtime_to_gtsc() (try 2)

This mostly reverts commit eb60be3d ("x86: don't pass negative time to
gtime_to_gtsc()") and instead corrects __update_vcpu_system_time()'s
handling of this_cpu(cpu_time).stime_local_stamp dating back before the
start of a HVM guest (which would otherwise lead to a negative value
getting passed to gtime_to_gtsc(), causing scale_delta() to produce
meaningless output).

Flushing the value to zero was wrong, and printing a message for
something that can validly happen wasn't very useful either.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
master commit: 5ad914bc867c5a6a4957869c89918f4e1f9dd9c4
master date: 2013-07-02 08:48:03 +0200

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index a176b88df627cba623769951e286b58259a96346..c2fc955183579f7ec4ee86bf3346759875909151 100644 (file)
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -823,16 +823,13 @@ static void __update_vcpu_system_time(struct vcpu *v, int force)
             struct pl_time *pl = &v->domain->arch.hvm_domain.pl_time;
 
             stime += pl->stime_offset + v->arch.hvm_vcpu.stime_offset;
-            if ( (s64)stime < 0 )
-            {
-                printk(XENLOG_G_WARNING "d%dv%d: bogus time %" PRId64
-                       " (offsets %" PRId64 "/%" PRId64 ")\n",
-                       d->domain_id, v->vcpu_id, stime,
-                      pl->stime_offset, v->arch.hvm_vcpu.stime_offset);
-                stime = 0;
-            }
+            if ( stime >= 0 )
+                tsc_stamp = gtime_to_gtsc(d, stime);
+            else
+                tsc_stamp = -gtime_to_gtsc(d, -stime);
         }
-        tsc_stamp = gtime_to_gtsc(d, stime);
+        else
+            tsc_stamp = gtime_to_gtsc(d, stime);
     }
     else
     {