On 2024/7/1 15:44, Jan Beulich wrote:
> On 30.06.2024 14:33, 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 removal device path to unmap pirq.
>> And add a new check to prevent (un)map when the subject domain
>> has no X86_EMU_USE_PIRQ flag.
>>
>> So that the interrupt of a passthrough device can be
>> successfully mapped to pirq for domU with X86_EMU_USE_PIRQ flag
>> when dom0 is PVH
>>
>> Signed-off-by: Jiqian Chen <jiqian.c...@amd.com>
>> Signed-off-by: Huang Rui <ray.hu...@amd.com>
>> Signed-off-by: Jiqian Chen <jiqian.c...@amd.com>
>> Reviewed-by: Stefano Stabellini <sstabell...@kernel.org>
>
> You keep carrying this R-b, despite making functional changes. This can't be
> quite right.
Will remove in next version.
>
> While functionally I'm now okay with the change, I still have a code structure
> concern:
>
>> --- a/xen/arch/x86/physdev.c
>> +++ b/xen/arch/x86/physdev.c
>> @@ -323,6 +323,13 @@ ret_t do_physdev_op(int cmd,
>> XEN_GUEST_HANDLE_PARAM(void) arg)
>> if ( !d )
>> break;
>>
>> + /* Prevent mapping when the subject domain has no X86_EMU_USE_PIRQ
>> */
>> + if ( is_hvm_domain(d) && !has_pirq(d) )
>> + {
>> + rcu_unlock_domain(d);
>> + return -EOPNOTSUPP;
>> + }
>> +
>> ret = physdev_map_pirq(d, map.type, &map.index, &map.pirq, &msi);
>>
>> rcu_unlock_domain(d);
>> @@ -346,6 +353,13 @@ ret_t do_physdev_op(int cmd,
>> XEN_GUEST_HANDLE_PARAM(void) arg)
>> if ( !d )
>> break;
>>
>> + /* Prevent unmapping when the subject domain has no
>> X86_EMU_USE_PIRQ */
>> + if ( is_hvm_domain(d) && !has_pirq(d) )
>> + {
>> + rcu_unlock_domain(d);
>> + return -EOPNOTSUPP;
>> + }
>> +
>> ret = physdev_unmap_pirq(d, unmap.pirq);
>>
>> rcu_unlock_domain(d);
>
> If you did go look, you will have noticed that we use "return" in the middle
> of this function only very sparingly (when alternatives would result in more
> complicated code elsewhere). I think you want to avoid "return" here, too,
> and probably go even further and avoid the extra rcu_unlock_domain() as well.
> That's easily possible to arrange for (taking the latter case as example):
>
> /* Prevent unmapping when the subject domain has no X86_EMU_USE_PIRQ
> */
> if ( !is_hvm_domain(d) || has_pirq(d) )
> ret = physdev_unmap_pirq(d, unmap.pirq);
> else
> ret = -EOPNOTSUPP;
>
> rcu_unlock_domain(d);
>
> Personally I would even use a conditional operator here, but I believe
> others might dislike its use in situations like this one.
>
> The re-arrangement make a little more noticeable though that the comment
> isn't quite right either: PV domains necessarily have no
> X86_EMU_USE_PIRQ. Maybe "... has no notion of pIRQ"?
Or just like below?
/*
* Prevent unmapping when the subject hvm domain has no
* X86_EMU_USE_PIRQ
*/
if ( is_hvm_domain(d) && !has_pirq(d) )
ret = -EOPNOTSUPP;
else
ret = physdev_unmap_pirq(d, unmap.pirq);
>
> Jan
--
Best regards,
Jiqian Chen.
