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Re: [Xen-devel] [PATCH v2 for-4.12] x86/hvm: Fix bit checking for CR4 and MSR_EFER

On Mon, Jan 28, 2019 at 04:40:59PM +0000, Andrew Cooper wrote:
> Before the cpuid_policy logic came along, %cr4/EFER auditing on migrate-in was
> complicated, because at that point no CPUID information had been set for the
> guest.  Auditing against the host CPUID was better than nothing, but not
> ideal.
> Similarly at the time, PVHv1 lacked the "CPUID passed through from hardware"
> behaviour with PV guests had, and PVH dom0 had to be special-cased to be able
> to boot.
> Order of information in the migration stream is still an issue (hence we still
> need to keep the restore parameter to cope with a nested virt corner case in
> the %cr4 case), but since Xen 4.9, all domains start with a suitable CPUID
> policy, which is a more appropriate upper bound than host_cpuid_policy.
> Finally, reposition the UMIP logic as it is the only row out of order.
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

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

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