Re: [Xen-devel] [PATCH v3 for 4.5] x86/viridian: Freeze time reference counter when domain is paused

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.10.14 at 11:21, <paul.durrant@xxxxxxxxxx> wrote:
> In XenServer system test it has become apparent that versions of Windows
> that make use of the time reference counter enlightenment cannot cope with
> large jumps forward in the value read from the MSR. Specifically,
> suspending a very large domain took approx. 45 minutes to complete and
> when the domain was resumed it was discovered that the WMI (Windows
> Management Instrumentation) service had hung.
> 
> The reason a large jump forward is seen by the guest is that, when a guest
> is suspended, the guest stops running when the SCHEDOP_suspend hypercall is
> made, however the MSR value essentially keeps incrementing until the
> tool-stack issues DOMCTL_gethvmcontext.
> 
> This patch adds code to freeze the value of the time reference counter
> on domain pause and 'thaw' it on domain unpause, but only thaw it if the
> domain is not shutting down. The absolute value of the counter is then
> saved in the viridian domain context record. This prevents the guest OS
> from experiencing large jumps in the value of the MSR and has been shown
> to reliably fix the problem with WMI.
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

ARM maintainers: I was about to commit this patch when I noticed
that there still was no ack from any of you for this (trivial) addition:

> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -580,6 +580,18 @@ void arch_domain_destroy(struct domain *d)
>      free_xenheap_page(d->shared_info);
>  }
>  
> +void arch_domain_shutdown(struct domain *d)
> +{
> +}
> +
> +void arch_domain_pause(struct domain *d)
> +{
> +}
> +
> +void arch_domain_unpause(struct domain *d)
> +{
> +}
> +
>  static int is_guest_pv32_psr(uint32_t psr)
>  {
>      switch (psr & PSR_MODE_MASK)

Jan


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