Re: [Xen-devel] [PATCH v4 2/4] x86/compat: Test both PV and PVH guests for compat mode

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> 09/02/15 2:55 AM >>>
>On 08/27/2015 12:01 PM, Jan Beulich wrote:
>>>>> On 13.08.15 at 20:12, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>> @@ -777,7 +777,7 @@ int arch_set_info_guest(
>>>   
>>>       /* The context is a compat-mode one if the target domain is 
>>> compat-mode;
>>>        * we expect the tools to DTRT even in compat-mode callers. */
>>> -    compat = is_pv_32bit_domain(d);
>>> +    compat = is_pv_32bit_domain(d) || is_pvh_32bit_domain(d);
>> I continue to think that this should include a v->domain ==
>> current->domain check (to match behavior for HVM guests
>> from the tool stack perspective). Having looked at patch 4, I also
>> can't see how the tool stack is being made expect a non-native
>> guest context record in the 32-bit PVH case (i.e. I'd appreciate
>> if you could point out where that hides).
>
>For vcpu 0 current->domain is dom0 so I am not sure how this check would 
>work.
>
>For a 32-bit PVH guest the toolstack will place data into 
>vcpu_guest_context_x86_32_t (in vcpu_x86_32()) and so the hypervisor, 
>knowing that the guest is a compat one (based on the test above), will 
>access appropriate fields.
>
>This is not how HVM guests are started --- "classic" PVH behaves very 
>much like a PV guest, unlike what we are doing with no-dm PVH.

And I believe this to be wrong, and potentially getting in the way of the no-dm
work - Roger?

As to the reference to vcpu_x86_32() - by its name alone it is already clear
that this is after the determination of what bit width a guest to deal with, and
looking at xc_dom_32_pae I still can't see why PVH guests would (intentionally
and legitimately) be treated like PV rather than HVM ones (not to speak of the
fact that I don't think 32-bit PVH is in any way limited to PAE).

Jan


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