x86/AMD: Stop counters on VPMU save

Stop the counters during VPMU save operation since they shouldn't be
running when VPCU that controls them is not. This also makes it
unnecessary to check for overflow in context_restore()

Set LVTPC vector before loading the context during vpmu_restore().
Otherwise it is possible to trigger an interrupt without proper vector.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Dietmar Hahn <dietmar.hahn@ts.fujitsu.com>

xen/arch/x86/hvm/svm/vpmu.c

@@ -196,21 +196,10 @@ static inline void context_restore(struct vcpu *v)
     struct vpmu_struct *vpmu = vcpu_vpmu(v);
     struct amd_vpmu_context *ctxt = vpmu->context;
 
-    for ( i = 0; i < num_counters; i++ )
-        wrmsrl(ctrls[i], ctxt->ctrls[i]);
-
     for ( i = 0; i < num_counters; i++ )
     {
         wrmsrl(counters[i], ctxt->counters[i]);
-
-        /* Force an interrupt to allow guest reset the counter,
-        if the value is positive */
-        if ( is_overflowed(ctxt->counters[i]) && (ctxt->counters[i] > 0) )
-        {
-            gdprintk(XENLOG_WARNING, "VPMU: Force a performance counter "
-                "overflow interrupt!\n");
-            amd_vpmu_do_interrupt(0);
-        }
+        wrmsrl(ctrls[i], ctxt->ctrls[i]);
     }
 }
 
@@ -223,8 +212,8 @@ static void amd_vpmu_restore(struct vcpu *v)
            vpmu_is_set(vpmu, VPMU_RUNNING)) )
         return;
 
-    context_restore(v);
     apic_write(APIC_LVTPC, ctxt->hw_lapic_lvtpc);
+    context_restore(v);
 
     vpmu_set(vpmu, VPMU_CONTEXT_LOADED);
 }
@@ -236,10 +225,11 @@ static inline void context_save(struct vcpu *v)
     struct amd_vpmu_context *ctxt = vpmu->context;
 
     for ( i = 0; i < num_counters; i++ )
-        rdmsrl(counters[i], ctxt->counters[i]);
-
-    for ( i = 0; i < num_counters; i++ )
+    {
         rdmsrl(ctrls[i], ctxt->ctrls[i]);
+        wrmsrl(ctrls[i], 0);
+        rdmsrl(counters[i], ctxt->counters[i]);
+    }
 }
 
 static void amd_vpmu_save(struct vcpu *v)