Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit flags

Jacob Pan
2021-05-19T15:43:45Z

Hi Jason,

On Mon, 17 May 2021 11:37:58 -0300, Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Thu, May 13, 2021 at 04:40:28PM -0700, Jacob Pan wrote:
>
> > Looks like we are converging. Let me summarize the takeaways:
> > 1. Remove IOMMU_SVA_BIND_SUPERVISOR flag from this patch, in fact there
> > will be no flags at all for iommu_sva_bind_device()
> > 2. Remove all supervisor SVA related vt-d, idxd code.
> > 3. Create API iommu_setup_system_pasid_direct_map(option_flag)
> > if (option_flag == 1)
> > iommu_domain_alloc(IOMMU_DOMAIN_DMA);
> > if (option_flag == 2)
> > iommu_domain_alloc(IOMMU_DOMAIN_DIRECT); //new domain
> > type? setup IOMMU page tables mirroring the direct map
> > 4. Create API iommu_enable_dev_direct_map(struct dev, &pasid, &option)
> > - Drivers call this API to get the system PASID and which
> > option is available on the system PASID
> > - mark device as PASID only, perhaps a new flag in struct
> > device->dev_iommu->pasid_only = 1
> > 5. DMA API IOMMU vendor ops will take action based on the pasid_only
> > flag to decide if the mapping is for system PASID page tables.
> >
> > Does it make sense?
>
> I think you will run into trouble with that approach when you get to
> patches..
>
> For 'option 1' what you want is an API that is 'give me a PASID that
> is equivalent to the RID'.
>
> Then all the DMA API operations map IO page tables to both RID and
> PASID access. For the direct mode the PASID and RID will both point at
> the shared all physical memory IO page table.
>
> Otherwise the DMA API won't care if the device is using RID or PASID,
> if it needs to map a range it does it to the shared IO page table and
> flushes both the RID and PASID based caches.
>
> Then the driver will use the normal DMA API with its normal struct
> pci_device and simply tell the HW to do DMA TLP's with the returned
> PASID.
>
> For 'option 2' it should be a completely different API family.
>
Make sense, thanks for the suggestions.

> Jason

Thanks,

Jacob