Re: [Xen-devel] [PATCH for-4.10] tools/libxc: Fix restoration of PV MSRs after migrate

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Nov 16, 2017 at 09:13:22PM +0000, Andrew Cooper wrote:
> There are two bugs in process_vcpu_msrs() which clearly demonstrate that I
> didn't test this bit of Migration v2 very well when writing it...
> 
> vcpu->msrsz is always expected to be a multiple of xen_domctl_vcpu_msr_t
> records in a spec-compliant stream, so the modulo yields 0 for the msr_count,
> rather than the actual number sent in the stream.
> 
> Passing 0 for the msr_count causes the hypercall to exit early, and hides the
> fact that the guest handle is inserted into the wrong field in the domctl
> union.
> 
> The reason that these bugs have gone unnoticed for so long is that the only
> MSRs passed like this for PV guests are the AMD DBGEXT MSRs, which only exist
> in fairly modern hardware, and whose use doesn't appear to be implemented in
> any contemporary PV guests.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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