Re: [XEN PATCH v9 2/5] x86/pvh: Allow (un)map_pirq when dom0 is PVH

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2024/6/12 17:21, Jan Beulich wrote:
> On 12.06.2024 11:07, Chen, Jiqian wrote:
>> On 2024/6/12 16:53, Jan Beulich wrote:
>>> On 12.06.2024 04:43, Chen, Jiqian wrote:
>>>> On 2024/6/10 23:58, Jan Beulich wrote:
>>>>> On 07.06.2024 10:11, Jiqian Chen wrote:
>>>>>> If run Xen with PVH dom0 and hvm domU, hvm will map a pirq for
>>>>>> a passthrough device by using gsi, see qemu code
>>>>>> xen_pt_realize->xc_physdev_map_pirq and libxl code
>>>>>> pci_add_dm_done->xc_physdev_map_pirq. Then xc_physdev_map_pirq
>>>>>> will call into Xen, but in hvm_physdev_op, PHYSDEVOP_map_pirq
>>>>>> is not allowed because currd is PVH dom0 and PVH has no
>>>>>> X86_EMU_USE_PIRQ flag, it will fail at has_pirq check.
>>>>>>
>>>>>> So, allow PHYSDEVOP_map_pirq when dom0 is PVH and also allow
>>>>>> PHYSDEVOP_unmap_pirq for the failed path to unmap pirq. And
>>>>>> add a new check to prevent self map when subject domain has no
>>>>>> PIRQ flag.
>>>>>>
>>>>>> Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
>>>>>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>>>>>> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>>>>>
>>>>> What's imo missing in the description is a clarification / justification 
>>>>> of
>>>>> why it is going to be a good idea (or at least an acceptable one) to 
>>>>> expose
>>>>> the concept of PIRQs to PVH. If I'm not mistaken that concept so far has
>>>>> been entirely a PV one.
>>>> I didn't want to expose the concept of PIRQs to PVH.
>>>> I did this patch is for HVM that use PIRQs, what I said in commit message 
>>>> is HVM will map a pirq for gsi, not PVH.
>>>> For the original code, it checks " !has_pirq(currd)", but currd is PVH 
>>>> dom0, so it failed. So I need to allow PHYSDEVOP_map_pirq
>>>> even currd has no PIRQs, but the subject domain has.
>>>
>>> But that's not what you're enforcing in do_physdev_op(). There you only
>>> prevent self-mapping. If I'm not mistaken all you need to do is drop the
>>> "d == current->domain" checks from those conditionals.
>> What I want is to allow PHYSDEVOP_map_pirq when currd doesn't have PIRQs, 
>> but subject domain has.
>> Then I just add "break" in hvm_physdev_op without any checks, that will 
>> cause self-mapping problems.
>> And in previous mail thread, you suggested me to prevent self-mapping when 
>> subject domain doesn't have PIRQs.
>> So I added checks in do_physdev_op.
> 
> Self-mapping was a primary concern of mine. Yet why deal with only a subset
> of what needs preventing, when generalizing things actually can be done by
> having less code.
Make sense. I will rebase the branch once your codes are merged.

> 
> Jan

-- 
Best regards,
Jiqian Chen.