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

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

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.

> 
>> --- a/xen/arch/x86/hvm/hypercall.c
>> +++ b/xen/arch/x86/hvm/hypercall.c
>> @@ -71,8 +71,14 @@ long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
>> arg)
>>  
>>      switch ( cmd )
>>      {
>> +    /*
>> +     * Only being permitted for management of other domains.
>> +     * Further restrictions are enforced in do_physdev_op.
>> +     */
>>      case PHYSDEVOP_map_pirq:
>>      case PHYSDEVOP_unmap_pirq:
>> +        break;
> 
> Nit: Imo such a comment ought to be indented like code (statements), not
> like the case labels.
Thanks, I will change in next version.

> 
> Jan

-- 
Best regards,
Jiqian Chen.