Re: [Xen-devel] [PATCH for-4.12] x86/hvm: Fix hvm_cr4_guest_valid_bits() for PVH dom0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.01.19 at 16:36, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 28/01/2019 15:22, Jan Beulich wrote:
>>>>> On 28.01.19 at 14:56, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> Before the cpuid_policy logic came along, %cr4 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.
>>>
>>> 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),
>>> but since Xen 4.9, the domain starts with the applicable max policy, which 
> is
>>> a more appropriate upper bound than the host cpuid policy.
>>>
>>> This also makes the fix from c/s 9d2efbafb8 obsolete, as not even dom0 
> starts
>>> without a policy.
>> While I agree with the change itself, I'm struggling to make a connection
>> from this description to what was actually wrong for PVH Dom0. You
>> mostly talk about migration, which is not relevant do Dom0 as an object
>> (and I don't see a connection to domains being migrated by PVH Dom0).
> 
> The PVH Dom0 angle is simply that it is wrong to audit against the host
> policy.

So I'd appreciate if you could make the connection a little more
explicit. In any event
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan



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