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

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.


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