Re: [Xen-devel] [PATCH 2/4] tools/libxc: Use an explicit check for PV MSRs in xc_domain_save()

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-06-06 at 10:44 +0100, Andrew Cooper wrote:
> On 06/06/14 10:15, Ian Campbell wrote:
> > On Thu, 2014-06-05 at 16:57 +0100, Andrew Cooper wrote:
> >> To avoid a race condition with the vcpu touching a new MSR between the
> >> two hypercalls, Xen must return the maximum possible msr_count with the
> >> request for size, so the toolstack can guarantee to allocate a large
> >> enough buffer.
> > If the msr_count returned a build time constant can't it just be part of
> > the interface then? Either as #define or an explicitly sized array type
> > somewhere.
> >
> > Ian.
> >
> 
> The maximum possible msr_count depends on architecture, features
> available and, plausibly, domain cpuid policy.
> 
> At the moment it is trivial, Intel = 0 and AMD = {0, 4}, but this will
> get more complicated as we add support for more MSRs.
> 
> The information does have to be made available on a per-domain basis.

OK then.

Ian.



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