Re: [RFC] iommu_ops->domain_alloc_paging() enhancement to support AMD IOMMU driver

[Yi Liu <yi.l.liu@intel.com>]

On 2024/7/12 09:39, Baolu Lu wrote:
> On 7/11/24 9:56 PM, Yi Liu wrote:
>>
>>> For UNMANAGED domain (like vfio-pci), we would need a indication from 
>>> core layer
>>> saying whether we want to allocate PASID capable domain or not. So that
>>> internally we can allocate appropriate page table type.
>>>
>>> That means from VFIO layer we need to pass this detail to IOMMU layer.
>>> For this part, I will start watching your patch. May be we can start 
>>> discussion
>>> in that thread itself.
>>>
>>
>> yeah. Looks like you need to pass a hint to iommu driver for domain
>> allocation. For the usage vfio+iommufd, it is fine as the domain_alloc_user
>> accepts a flag. For legacy vfio (using vfio iommu type1) usage, it's a bit
>> tough as the domain allocation is within kernel, userspace does not have
>> any input on it so far. And vfio type1 does not expose the domain concept
>> to userspace, it only exposes container which is kind of an address space
>> object. This means no good way for userspace to control the domain
>> allocation.
>>
>> If it's only a matter when PASID is enabled, perhaps we can skip vfio iommu
>> type1 as it is not supposed to support PASID.
> 
> As we have already agreed that new features should go through IOMMUFD
> and vfio/type1 is only kept for legacy compatible purpose, I don't think
> we need to carry any PASID bits in the vifo path. Did I miss anything?

yes, we do. I have below kdoc for it in my pasid series [1]. Let's wait for
Vasant's confirmation if it's only a matter of pasid. It's not quite clear
to me based on my limited AMD iommu knowledge yet. :)

+ * Associate a pasid (of a cdev device) with an address space within the
+ * bound iommufd. Undo by VFIO_DEVICE_PASID_DETACH_IOMMUFD_PT or device fd
+ * close. This is only allowed on cdev fds.

[1] https://lore.kernel.org/kvm/20240412082121.33382-4-yi.l.liu@intel.com/

-- 
Regards,
Yi Liu