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

Baolu Lu
2022-05-25T02:38:35Z

On 2022/5/25 08:44, Tian, Kevin wrote:
>> From: Jason Gunthorpe <jgg@nvidia.com>
>> Sent: Tuesday, May 24, 2022 9:39 PM
>>
>> On Tue, May 24, 2022 at 09:39:52AM +0000, Tian, Kevin wrote:
>>>> From: Lu Baolu <baolu.lu@linux.intel.com>
>>>> Sent: Thursday, May 19, 2022 3:21 PM
>>>>
>>>> The iommu_sva_domain represents a hardware pagetable that the
>> IOMMU
>>>> hardware could use for SVA translation. This adds some infrastructure
>>>> to support SVA domain in the iommu common layer. It includes:
>>>>
>>>> - Add a new struct iommu_sva_domain and new IOMMU_DOMAIN_SVA
>>>> domain
>>>> type.
>>>> - Add a new domain ops pointer in iommu_ops. The IOMMU drivers that
>>>> support SVA should provide the callbacks.
>>>> - Add helpers to allocate and free an SVA domain.
>>>> - Add helpers to set an SVA domain to a device and the reverse
>>>> operation.
>>>>
>>>> Some buses, like PCI, route packets without considering the PASID value.
>>>> Thus a DMA target address with PASID might be treated as P2P if the
>>>> address falls into the MMIO BAR of other devices in the group. To make
>>>> things simple, the attach/detach interfaces only apply to devices
>>>> belonging to the singleton groups, and the singleton is immutable in
>>>> fabric i.e. not affected by hotplug.
>>>>
>>>> The iommu_set/block_device_pasid() can be used for other purposes,
>>>> such as kernel DMA with pasid, mediation device, etc. Hence, it is put
>>>> in the iommu.c.
>>>
>>> usually we have 'set/clear' pair or 'allow/block'. Having 'set' paired
>>> with 'block' doesn't read very clearly.
>>
>> I thought we agreed we'd use the blocking domain for this? Why did it
>> go back to an op?
>>
>
> Probably it's based on following discussion:
>
> https://lore.kernel.org/all/c8492b29-bc27-ae12-d5c4-9fbbc797e310@linux.intel.com/
>
> --
>> FWIW from my point of view I'm happy with having a .detach_dev_pasid op
>> meaning implicitly-blocked access for now.
>
> If this is the path then lets not call it attach/detach
> please. 'set_dev_pasid' and 'set_dev_blocking_pasid' are clearer
> names.

Yes. Learning from above discussion, we are about to implement the
set_dev_pasid and blocking domain in parallel. We will convert all
the callback names to set_dev and set_dev_pasid after blocking domain
support is merged.

> --
>
> Looks Baolu chooses this path and plans to use the blocking domain
> later.

Yes. I have already started to implement the blocking domain in Intel
driver. With it as an example, we can extend it to other possible IOMMU
drivers.

Best regards,
baolu