Re: [PATCH v7 03/10] iommu/sva: Add iommu_sva_domain support

Robin Murphy
2022-05-25T10:08:20Z

On 2022-05-25 07:20, Baolu Lu wrote:
> Hi Robin,
>
> On 2022/5/24 22:36, Robin Murphy wrote:
>> On 2022-05-19 08:20, Lu Baolu wrote:
>> [...]
>>> diff --git a/drivers/iommu/iommu-sva-lib.c
>>> b/drivers/iommu/iommu-sva-lib.c
>>> index 106506143896..210c376f6043 100644
>>> --- a/drivers/iommu/iommu-sva-lib.c
>>> +++ b/drivers/iommu/iommu-sva-lib.c
>>> @@ -69,3 +69,51 @@ struct mm_struct *iommu_sva_find(ioasid_t pasid)
>>>       return ioasid_find(&iommu_sva_pasid, pasid, __mmget_not_zero);
>>>   }
>>>   EXPORT_SYMBOL_GPL(iommu_sva_find);
>>> +
>>> +/*
>>> + * IOMMU SVA driver-oriented interfaces
>>> + */
>>> +struct iommu_domain *
>>> +iommu_sva_alloc_domain(struct bus_type *bus, struct mm_struct *mm)
>>
>> Argh, please no new bus-based external interfaces! Domain allocation
>> needs to resolve to the right IOMMU instance to solve a number of
>> issues, and cleaning up existing users of iommu_domain_alloc() to
>> prepare for that is already hard enough. This is arguably even more
>> relevant here than for other domain types, since SVA support is more
>> likely to depend on specific features that can vary between IOMMU
>> instances even with the same driver. Please make the external
>> interface take a struct device, then resolve the ops through dev->iommu.
>>
>> Further nit: the naming inconsistency bugs me a bit -
>> iommu_sva_domain_alloc() seems more natural. Also I'd question the
>> symmetry vs. usability dichotomy of whether we *really* want two
>> different free functions for a struct iommu_domain pointer, where any
>> caller which might mix SVA and non-SVA usage then has to remember how
>> they allocated any particular domain :/
>>
>>> +{
>>> +    struct iommu_sva_domain *sva_domain;
>>> +    struct iommu_domain *domain;
>>> +
>>> +    if (!bus->iommu_ops || !bus->iommu_ops->sva_domain_ops)
>>> +        return ERR_PTR(-ENODEV);
>>> +
>>> +    sva_domain = kzalloc(sizeof(*sva_domain), GFP_KERNEL);
>>> +    if (!sva_domain)
>>> +        return ERR_PTR(-ENOMEM);
>>> +
>>> +    mmgrab(mm);
>>> +    sva_domain->mm = mm;
>>> +
>>> +    domain = &sva_domain->domain;
>>> +    domain->type = IOMMU_DOMAIN_SVA;
>>> +    domain->ops = bus->iommu_ops->sva_domain_ops;
>>
>> I'd have thought it would be logical to pass IOMMU_DOMAIN_SVA to the
>> normal domain_alloc call, so that driver-internal stuff like context
>> descriptors can be still be hung off the domain as usual (rather than
>> all drivers having to implement some extra internal lookup mechanism
>> to handle all the SVA domain ops), but that's something we're free to
>> come
>
> Agreed with above comments. Thanks! I will post an additional patch
> for review later.
>
>> back and change later. FWIW I'd just stick the mm pointer in struct
>> iommu_domain, in a union with the fault handler stuff and/or
>> iova_cookie - those are mutually exclusive with SVA, right?
>
> "iova_cookie" is mutually exclusive with SVA, but I am not sure about
> the fault handler stuff.

To correct myself, the IOVA cookie should be irrelevant to *current*
SVA, but if we ever get as far as whole-device-SVA without PASIDs then
we might need an MSI cookie (modulo the additional problem of stealing
some procvess address space for it).

> Did you mean @handler and @handler_token staffs below?
>
> struct iommu_domain {
>         unsigned type;
>         const struct iommu_domain_ops *ops;
>         unsigned long pgsize_bitmap;    /* Bitmap of page sizes in use */
>         iommu_fault_handler_t handler;
>         void *handler_token;
>         struct iommu_domain_geometry geometry;
>         struct iommu_dma_cookie *iova_cookie;
> };
>
> Is it only for DMA domains? From the point view of IOMMU faults, it
> seems to be generic.

Yes, it's the old common iommu_set_fault_handler() stuff (which arguably
is more of a "notifier" than a "handler"), but I assume that that's
irrelevant if SVA is using IOPF instead?

Thanks,
Robin.