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

Baolu Lu
2022-05-25T06:20:42Z

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.

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.

Best regards,
baolu