Re: [PATCH v2 02/19] iommufd/viommu: Add IOMMUFD_OBJ_VIOMMU and IOMMU_VIOMMU_ALLOC ioctl
From: Jason Gunthorpe <jgg@nvidia.com>
Date: 2024-09-04 16:26:26
Also in:
linux-iommu, linux-kselftest, lkml
On Sun, Sep 01, 2024 at 10:27:09PM -0700, Nicolin Chen wrote:
On Sun, Sep 01, 2024 at 10:39:17AM +0800, Baolu Lu wrote:quoted
On 2024/8/28 0:59, Nicolin Chen wrote:quoted
+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.
Eventually you need a way to pin the physical iommu, without pinning any idevs. Not sure how best to do that Jason