Re: [Xen-devel] [PATCH] x86/time: Correctly update the domain watchdog in the shared info page

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 16/07/2013 10:51, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote:

> For a normal HVM domain on 64bit Xen, the shared info switches to 32bit for
> hvmloader, then to the native size for the HVM guest.  This guarantees at
> least one transition during which the wallclock information will be updated.
> 
> The wallclock for each domain gets updated when dom0 issues a XENPF_settime
> hypercall to updated the wallclock base time.
> 
> However, for a 64bit domain on 64bit Xen which is resuming from S4,
> (i.e. bypassing hvmloader), there are no transitions in the size of the shared
> info page, meaning that before the next XENPF_settime from dom0, the domU PV
> drivers will find the Unix Epoch in the wallclock rather than the correct
> time.
> 
> Therefore, manually set the watchdog when creating the domain, so it is set
> right from the start of the domain, and when manually adjusting the domain
> time offset, as it depends on the same value which has just been adjusted.

s/watchdog/wallclock/

Also I wonder if this is not fixed by f8e8fd56 already? Not that I'm averse
to throwing in a few more update_domain_wallclock_time() calls if they are
useful.

 -- Keir

> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Keir Fraser <keir@xxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> ---
> This fixes a bug presence since Xen gained 64bit support, which had been
> hacked around in a gross way in XenServer.
> 
> It should be backported to all stable releases.
> ---
>  xen/arch/x86/domain.c |    1 +
>  xen/arch/x86/time.c   |    1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
> index 874742c..664d598 100644
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -546,6 +546,7 @@ int arch_domain_create(struct domain *d, unsigned int
> domcr_flags)
>          clear_page(d->shared_info);
>          share_xen_page_with_guest(
>              virt_to_page(d->shared_info), d, XENSHARE_writable);
> +        update_domain_wallclock_time(d);
>  
>          if ( (rc = init_domain_irq_mapping(d)) != 0 )
>              goto fail;
> diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> index cf8bc78..f047cb3 100644
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -931,6 +931,7 @@ void domain_set_time_offset(struct domain *d, int32_t
> time_offset_seconds)
>      d->time_offset_seconds = time_offset_seconds;
>      if ( is_hvm_domain(d) )
>          rtc_update_clock(d);
> +    update_domain_wallclock_time(d);
>  }
>  
>  int cpu_frequency_change(u64 freq)



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