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

[Diana Crisan <dcrisan@flexiant.com>]

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 Monné <roger.pau@citrix.com>
> Cc: Keir Fraser <keir@xen.org>
> Cc: Jan Beulich <jbeulich@suse.com>
> Cc: George Dunlap <george.dunlap@eu.citrix.com>
Tested-By: Diana Crisan  <dcrisan@flexiant.com>
> ---
> 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').

Thanks,
Diana

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