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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

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.

 -George


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