On 2024/12/12 13:51, Tian, Kevin wrote:
From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
Sent: Thursday, December 12, 2024 11:15 AM
On 2024/12/11 16:46, Tian, Kevin wrote:
From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
Sent: Tuesday, December 10, 2024 11:15 AM
On 2024/12/9 22:57, Jason Gunthorpe wrote:
We want some reasonable compromise to encourage applications to use
IOMMU_HWPT_ALLOC_PASID properly, but not build too much
complexity
to
reject driver-specific behavior.
I'm ok to do it in iommufd as long as it is only applicable to hwpt_paging.
Otherwise, attaching nested domain to pasid would be failed according to
the aforementioned enforcement.
IMHO we may want to have a general enforcement in IOMMUFD that
any domain (paging or nested) must have ALLOC_PASID set to be
used in pasid-oriented operations.
drivers can have more restrictions, e.g. for arm/amd allocating a nested
domain with that bit set will fail at the beginning.
ARM/AMD should allow allocating nested domain with this flag. Otherwise,
it does not suit the ALLOC_PASID definition. It requires both the PASID
path and non-PASID path to use pasid-compat domain.
hmm the main point you raised at the beginning was that ARM/AMD
doesn't support the flag on nested domain, given the CD/PASID table
is a per-RID thing.
yes.
So maybe we should not stick with the initial purpose of ALLOC_PASID flag.
It actually means selecting V2 page table. But the definition of it allows
us to consider the nested domains to be pasid-compat as Intel allows it.
And, a sane userspace running on ARM/AMD will never attach nested
domain
to PASIDs. Even it does, the ARM SMMU and AMD iommu driver can fail such
attempts. In this way, we can enforce the ALLOC_PASID flag for any domains
used by PASID-capable devices in iommufd. This suits the existing
ALLOC_PASID definition as well.
Isn't it what I was suggesting? IOMMUFD just enforces that flag must
be set if a domain will be attached to PASID, and drivers will do
additional restrictions e.g. AMD/ARM allows the flag only on paging
domain while VT-d allows it for any type.
A slight difference. :) I think we also need to enforce it for the
non-PASID path. If not, the PASID path cannot work according to the
ALLOC_PASID definition. But we are on the same page about the additional
restrictions in ARM/AMD drivers about the nested domain used on PASIDs.
This is supposed to be done in attach phase instead of domain allocation
time.
--
Regards,
Yi Liu
