[PATCH v2 5/5] vfio/iommu_type1: Simplify group attachment

[Robin Murphy]

On 2022-06-17 03:53, Tian, Kevin wrote:
>> From: Nicolin Chen <nicolinc at nvidia.com>
>> Sent: Friday, June 17, 2022 6:41 AM
>>
>>> ...
>>>> -     if (resv_msi) {
>>>> +     if (resv_msi && !domain->msi_cookie) {
>>>>                ret = iommu_get_msi_cookie(domain->domain,
>>>> resv_msi_base);
>>>>                if (ret && ret != -ENODEV)
>>>>                        goto out_detach;
>>>> +             domain->msi_cookie = true;
>>>>        }
>>>
>>> why not moving to alloc_attach_domain() then no need for the new
>>> domain field? It's required only when a new domain is allocated.
>>
>> When reusing an existing domain that doesn't have an msi_cookie,
>> we can do iommu_get_msi_cookie() if resv_msi is found. So it is
>> not limited to a new domain.
> 
> Looks msi_cookie requirement is per platform (currently only
> for smmu. see arm_smmu_get_resv_regions()). If there is
> no mixed case then above check is not required.
> 
> But let's hear whether Robin has a different thought here.

Yes, the cookie should logically be tied to the lifetime of the domain 
itself. In the relevant context, "an existing domain that doesn't have 
an msi_cookie" should never exist.

Thanks,
Robin.