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 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.

> 
> Further see also
> https://lists.xen.org/archives/html/xen-devel/2024-06/msg00540.html.
> 
> Jan

-- 
Best regards,
Jiqian Chen.