Re: [PATCH] iommu/amd: Add Secure ATS support

[Baolu Lu <baolu.lu@linux.intel.com>]

On 3/4/25 22:18, Jason Gunthorpe wrote:
> On Tue, Mar 04, 2025 at 10:16:45AM +0800, Baolu Lu wrote:
>> For ATS enablement, I believe we have already reached some agreement
>> that ATS enablement is in an on-demand manner. ATS is enabled when the
>> first domain that requires ATS is attached and disabled when the last
>> domain is detached. That matches what we are doing for PRI.
> It is not quite so simple, we need ATS in some virtualization cases
> for VFIO even though it is not "using" ATS for PRI.

In such cases, perhaps we could allocate a domain-allocation flag for
this purpose. Userspace would opt-in to this flag when allocating the
iommufd hwpt.

> 
> Today the iommu drivers always enable ATS for paging domains if ATS is
> supported. This is what I'm wondering if it should be made optional

The domain-allocation flag also applies here. The iommu core manages the
policy and determines whether to pass the ATS-required flag to the
domain allocation callback of the iommu drivers. The iommu core's sysfs
interface will include a node to modify the allocation policy.

Thanks,
baolu