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Re: [Xen-devel] [PATCH for-4.12] x86/hvm: Fix hvm_cr4_guest_valid_bits() for PVH dom0
- To: Wei Liu <wei.liu2@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 28 Jan 2019 15:29:48 +0000
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- Cc: Juergen Gross <jgross@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>
- Delivery-date: Mon, 28 Jan 2019 15:30:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 28/01/2019 15:22, Wei Liu wrote:
> On Mon, Jan 28, 2019 at 01:56:29PM +0000, Andrew Cooper 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.
>>
>> Finally, reposition the UMIP logic as it is the only row out of order.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> It is indeed the case that all x86 domains will get a cpuid policy,
> auditing against that makes more sense. But what about code in
> hvm_efer_valid? Why didn't you make it work with arch.cpuid?
Frankly, because I hadn't spotted it.
hvm_efer_valid() is rather harder to reason about with the cr0_pg
parameter, as it doubles as a restore boolean.
~Andrew
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