On Sun, Sep 01, 2024 at 10:39:17AM +0800, Baolu Lu wrote:
On 2024/8/28 0:59, Nicolin Chen wrote:
+int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd) +{
struct iommu_viommu_alloc *cmd = ucmd->cmd;struct iommufd_hwpt_paging *hwpt_paging;struct iommufd_viommu *viommu;struct iommufd_device *idev;int rc;if (cmd->flags)return -EOPNOTSUPP;idev = iommufd_get_device(ucmd, cmd->dev_id);Why does a device reference count is needed here? When is this reference count released after the VIOMMU is allocated?
Hmm, it was used to get dev->iommu->iommu_dev to pin the VIOMMU to a physical IOMMU instance (in v1). Jason suggested to remove that, yet I didn't realize that this idev is now completely useless.
With that being said, a parent HWPT could be shared across VIOMUs allocated for the same VM. So, I think we do need a dev pointer to know which physical instance the VIOMMU allocates for, especially for a driver-managed VIOMMU.
Perhaps we should add back the iommu_dev and properly refcount it.
Thanks Nicolin