[Xen-devel] [PATCH] rdtsc emulation (PV and HVM) must be monotonically increasing

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

The Intel SDM (section 18.10) clearly states that rdtsc
returns a "monotonically increasing unique value".
Current emulation code for rdtsc (both PV and HVM) returns
only a monotonically-non-decreasing (non-unique) value,
so ensure stale value is always incremented.

Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>

diff -r 8fc927798476 xen/arch/x86/hvm/vpt.c
--- a/xen/arch/x86/hvm/vpt.c    Tue Sep 01 11:36:51 2009 +0100
+++ b/xen/arch/x86/hvm/vpt.c    Tue Sep 01 16:53:42 2009 -0600
@@ -47,10 +47,10 @@ u64 hvm_get_guest_time(struct vcpu *v)
 
     spin_lock(&pl->pl_time_lock);
     now = get_s_time() + pl->stime_offset;
-    if ( (int64_t)(now - pl->last_guest_time) >= 0 )
+    if ( (int64_t)(now - pl->last_guest_time) > 0 )
         pl->last_guest_time = now;
     else
-        now = pl->last_guest_time;
+        now = ++pl->last_guest_time;
     spin_unlock(&pl->pl_time_lock);
 
     return now + v->arch.hvm_vcpu.stime_offset;
diff -r 8fc927798476 xen/arch/x86/time.c
--- a/xen/arch/x86/time.c       Tue Sep 01 11:36:51 2009 +0100
+++ b/xen/arch/x86/time.c       Tue Sep 01 16:53:42 2009 -0600
@@ -1454,10 +1454,10 @@ void pv_soft_rdtsc(struct vcpu *v, struc
         rdtsc_usercount++;
         spin_lock(&v->domain->arch.vtsc_lock);
         now = get_s_time() + v->domain->arch.vtsc_stime_offset;
-        if ( (int64_t)(now - v->domain->arch.vtsc_last) >= 0 )
+        if ( (int64_t)(now - v->domain->arch.vtsc_last) > 0 )
             v->domain->arch.vtsc_last = now;
         else
-            now = v->domain->arch.vtsc_last;
+            now = ++v->domain->arch.vtsc_last;
         spin_unlock(&v->domain->arch.vtsc_lock);
         regs->eax = (uint32_t)now;
         regs->edx = (uint32_t)(now >> 32);

Attachment: vtsc-mono.patch
Description: Binary data

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