Re: [RFC PATCH] iommu/xen: Add Xen PV-IOMMU driver

[Baolu Lu <baolu.lu@linux.intel.com>]

On 6/24/24 7:09 PM, Robin Murphy wrote:
> On 2024-06-23 4:21 am, Baolu Lu wrote:
>> On 6/21/24 11:09 PM, Teddy Astie wrote:
>>> Le 19/06/2024 à 18:30, Jason Gunthorpe a écrit :
>>>> On Thu, Jun 13, 2024 at 01:50:22PM +0000, Teddy Astie wrote:
>>>>
>>>>> +struct iommu_domain *xen_iommu_domain_alloc(unsigned type)
>>>>> +{
>>>>> +    struct xen_iommu_domain *domain;
>>>>> +    u16 ctx_no;
>>>>> +    int ret;
>>>>> +
>>>>> +    if (type & IOMMU_DOMAIN_IDENTITY) {
>>>>> +        /* use default domain */
>>>>> +        ctx_no = 0;
>>>> Please use the new ops, domain_alloc_paging and the static identity 
>>>> domain.
>>> Yes, in the v2, I will use this newer interface.
>>>
>>> I have a question on this new interface : is it valid to not have a
>>> identity domain (and "default domain" being blocking); well in the
>>> current implementation it doesn't really matter, but at some point, we
>>> may want to allow not having it (thus making this driver mandatory).
>>
>> It's valid to not have an identity domain if "default domain being
>> blocking" means a paging domain with no mappings.
>>
>> In the iommu driver's iommu_ops::def_domain_type callback, just always
>> return IOMMU_DOMAIN_DMA, which indicates that the iommu driver doesn't
>> support identity translation.
> 
> That's not necessary - if neither ops->identity_domain nor 
> ops->domain_alloc(IOMMU_DOMAIN_IDENTITY) gives a valid domain then we 
> fall back to IOMMU_DOMAIN_DMA anyway.

Yes. That's true.

Best regards,
baolu