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

["Roger Pau Monné" <roger.pau@citrix.com>]

El 02/09/15 a les 10.08, Jan Beulich ha escrit:
>>>> Boris Ostrovsky <boris.ostrovsky@oracle.com> 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@oracle.com> 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?

The no-dm work doesn't use arch_set_info_guest, it uses a new function
created specifically for no-dm guests with a new structure also, see:

http://marc.info/?l=xen-devel&m=144017739531928

So I don't think this code is explicitly getting in the way of no-dm.
Another thing to consider might be if it's worth to add this when no-dm
is going in a complete different direction regarding AP startup. I
certainly don't plan to add classic PVH 32bit support to FreeBSD.

Roger.