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

On 05/06/13 13:02, Diana Crisan wrote:
On 04/06/13 16:32, Roger Pau Monne wrote:
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>
Tested-By: Diana Crisan  <dcrisan@xxxxxxxxxxxx>
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)

I have tested this patch and I have not been able to reproduce the guest stuck-clock problem we were seeing before (see *HVM Migration of domU on Qemu-upstream DM causes stuck system clock with ACPI* for details of the problem). Note: this was tested without the temporary fix to our problem ( which is specifying tsc_mode='native_paravirt').

Great, thanks Diana.


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