On 4/26/25 13:58, Nicolin Chen wrote:
NVIDIA Virtual Command Queue is one of the iommufd users exposing vIOMMU
features to user space VMs. Its hardware has a strict rule when mapping
and unmapping multiple global CMDQVs to/from a VM-owned VINTF, requiring
mappings in ascending order and unmappings in descending order.
The tegra241-cmdqv driver can apply the rule for a mapping in the LVCMDQ
allocation handler, however it can't do the same for an unmapping since
the destroy op returns void.
The key point is that unmapping happens during object destroy. These
depend/undepend helpers ensure a vCMDQ is not destroyed (and therefore
unmapped) before any vCMDQs that depend on it. Do I get it right?
Add iommufd_vcmdq_depend/undepend() for-driver helpers, allowing LVCMDQ
allocator to refcount_inc() a sibling LVCMDQ object and LVCMDQ destroyer
to refcount_dec().
This is a bit of compromise, because a driver might end up with abusing
the API that deadlocks the objects. So restrict the API to a dependency
between two driver-allocated objects of the same type, as iommufd would
unlikely build any core-level dependency in this case.
Signed-off-by: Nicolin Chen<nicol...@nvidia.com>
... if that's right,
Reviewed-by: Lu Baolu <baolu...@linux.intel.com>
Thanks,
baolu
