[Xen-devel] [PATCH v3] x86/vtsc: update vcpu_time in hvm_set_guest_time

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

When using a vtsc, hvm_set_guest_time changes hvm_vcpu.stime_offset,
which is used in the vcpu time structure to calculate the
tsc_timestamp, so after updating stime_offset we need to propagate the
change to vcpu_time in order for the guest to get the right time if
using the PV clock.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
Changes since v2:
 * Check for v == current instead of v->is_running to know if the vcpu
   is running.
Changes since v1:
 * Perform the call to update_vcpu_system_time in hvm_set_guest_time
   if the offset has changed and the vCPU is running.
---
 xen/arch/x86/hvm/vpt.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/xen/arch/x86/hvm/vpt.c b/xen/arch/x86/hvm/vpt.c
index 8dee662..4b1e1a3 100644
--- a/xen/arch/x86/hvm/vpt.c
+++ b/xen/arch/x86/hvm/vpt.c
@@ -57,7 +57,18 @@ u64 hvm_get_guest_time(struct vcpu *v)
 
 void hvm_set_guest_time(struct vcpu *v, u64 guest_time)
 {
-    v->arch.hvm_vcpu.stime_offset += guest_time - hvm_get_guest_time(v);
+    u64 offset = guest_time - hvm_get_guest_time(v);
+
+    if ( offset ) {
+        v->arch.hvm_vcpu.stime_offset += offset;
+        /*
+         * If hvm_vcpu.stime_offset is updated make sure to
+         * also update vcpu time, since this value is used to
+         * calculate the TSC.
+         */
+        if ( v == current )
+            update_vcpu_system_time(v);
+    }
 }
 
 static int pt_irq_vector(struct periodic_time *pt, enum hvm_intsrc src)
-- 
1.7.7.5 (Apple Git-26)


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