Re: [PATCH v2 10/22] iommufd/viommmu: Add IOMMUFD_CMD_VCMDQ_ALLOC ioctl

On Fri, Apr 25, 2025 at 10:58:05PM -0700, Nicolin Chen wrote:

Introduce a new IOMMUFD_CMD_VCMDQ_ALLOC ioctl for user space to allocate a vCMDQ for a vIOMMU object. Simply increase the refcount of the vIOMMU.

Signed-off-by: Nicolin Chen nicolinc@nvidia.com

drivers/iommu/iommufd/iommufd_private.h | 2 + include/uapi/linux/iommufd.h | 41 +++++++++++ drivers/iommu/iommufd/main.c | 6 ++ drivers/iommu/iommufd/viommu.c | 94 +++++++++++++++++++++++++ 4 files changed, 143 insertions(+)

diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h index 79160b039bc7..b974c207ae8a 100644 --- a/drivers/iommu/iommufd/iommufd_private.h +++ b/drivers/iommu/iommufd/iommufd_private.h @@ -611,6 +611,8 @@ int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd); void iommufd_viommu_destroy(struct iommufd_object *obj); int iommufd_vdevice_alloc_ioctl(struct iommufd_ucmd *ucmd); void iommufd_vdevice_destroy(struct iommufd_object *obj); +int iommufd_vcmdq_alloc_ioctl(struct iommufd_ucmd *ucmd); +void iommufd_vcmdq_destroy(struct iommufd_object *obj); #ifdef CONFIG_IOMMUFD_TEST int iommufd_test(struct iommufd_ucmd *ucmd); diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h index cc90299a08d9..06a763fda47f 100644 --- a/include/uapi/linux/iommufd.h +++ b/include/uapi/linux/iommufd.h @@ -56,6 +56,7 @@ enum { IOMMUFD_CMD_VDEVICE_ALLOC = 0x91, IOMMUFD_CMD_IOAS_CHANGE_PROCESS = 0x92, IOMMUFD_CMD_VEVENTQ_ALLOC = 0x93,

• IOMMUFD_CMD_VCMDQ_ALLOC = 0x94,

}; /** @@ -1147,4 +1148,44 @@ struct iommu_veventq_alloc { __u32 __reserved; }; #define IOMMU_VEVENTQ_ALLOC _IO(IOMMUFD_TYPE, IOMMUFD_CMD_VEVENTQ_ALLOC)

+/**

• • enum iommu_vcmdq_type - Virtual Command Queue Type
• • @IOMMU_VCMDQ_TYPE_DEFAULT: Reserved for future use
• */

+enum iommu_vcmdq_type {

• IOMMU_VCMDQ_TYPE_DEFAULT = 0,

+};

+/**

• • struct iommu_vcmdq_alloc - ioctl(IOMMU_VCMDQ_ALLOC)
• • @size: sizeof(struct iommu_vcmdq_alloc)
• • @flags: Must be 0
• • @viommu_id: Virtual IOMMU ID to associate the virtual command queue with
• • @type: One of enum iommu_vcmdq_type
• • @index: The logical index to the virtual command queue per virtual IOMMU, for

• •     a multi-queue model
    

• • @out_vcmdq_id: The ID of the new virtual command queue
• • @addr: Base address of the queue memory in the guest physical address space
• • @length: Length of the queue memory in the guest physical address space
• • Allocate a virtual command queue object for a vIOMMU-specific HW-accelerated
• • feature that can access a guest queue memory described by @addr and @length.
• • It's suggested for VMM to back the queue memory using a single huge page with
• • a proper alignment for its contiguity in the host physical address space. The
• • call will fail, if the queue memory is not contiguous in the physical address
• • space. Upon success, its underlying physical pages will be pinned to prevent
• • VMM from unmapping them in the IOAS, until the virtual CMDQ gets destroyed.
• */

+struct iommu_vcmdq_alloc {

• __u32 size;
• __u32 flags;
• __u32 viommu_id;
• __u32 type;
• __u32 index;
• __u32 out_vcmdq_id;
• __aligned_u64 addr;
• __aligned_u64 length;

+}; +#define IOMMU_VCMDQ_ALLOC _IO(IOMMUFD_TYPE, IOMMUFD_CMD_VCMDQ_ALLOC) #endif diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c index 2b9ee9b4a424..ac51d5cfaa61 100644 --- a/drivers/iommu/iommufd/main.c +++ b/drivers/iommu/iommufd/main.c @@ -303,6 +303,7 @@ union ucmd_buffer { struct iommu_ioas_map map; struct iommu_ioas_unmap unmap; struct iommu_option option;

• struct iommu_vcmdq_alloc vcmdq; struct iommu_vdevice_alloc vdev; struct iommu_veventq_alloc veventq; struct iommu_vfio_ioas vfio_ioas;

@@ -358,6 +359,8 @@ static const struct iommufd_ioctl_op iommufd_ioctl_ops[] = { IOCTL_OP(IOMMU_IOAS_UNMAP, iommufd_ioas_unmap, struct iommu_ioas_unmap, length), IOCTL_OP(IOMMU_OPTION, iommufd_option, struct iommu_option, val64),

• IOCTL_OP(IOMMU_VCMDQ_ALLOC, iommufd_vcmdq_alloc_ioctl,

•  struct iommu_vcmdq_alloc, length),
  

  IOCTL_OP(IOMMU_VDEVICE_ALLOC, iommufd_vdevice_alloc_ioctl, struct iommu_vdevice_alloc, virt_id), IOCTL_OP(IOMMU_VEVENTQ_ALLOC, iommufd_veventq_alloc,

@@ -501,6 +504,9 @@ static const struct iommufd_object_ops iommufd_object_ops[] = { [IOMMUFD_OBJ_IOAS] = { .destroy = iommufd_ioas_destroy, },

• [IOMMUFD_OBJ_VCMDQ] = {

• .destroy = iommufd_vcmdq_destroy,
  

• }, [IOMMUFD_OBJ_VDEVICE] = { .destroy = iommufd_vdevice_destroy, },

When do we expect the VMM to use this ioctl? While it's spawning a new VM? IIUC, one vintf can have multiple lvcmdqs and looking at the series it looks like the vcmdq_alloc allocates a single lvcmdq. Is the plan to dedicate one lvcmdq to per VM? Which means VMs can share a vintf? Or do we plan to trap access to trap the access everytime the VM accesses an lvcmdq base register?

diff --git a/drivers/iommu/iommufd/viommu.c b/drivers/iommu/iommufd/viommu.c index a65153458a26..02a111710ffe 100644 --- a/drivers/iommu/iommufd/viommu.c +++ b/drivers/iommu/iommufd/viommu.c @@ -170,3 +170,97 @@ int iommufd_vdevice_alloc_ioctl(struct iommufd_ucmd *ucmd) iommufd_put_object(ucmd->ictx, &viommu->obj); return rc; }

+void iommufd_vcmdq_destroy(struct iommufd_object *obj) +{

• struct iommufd_vcmdq *vcmdq =

• container_of(obj, struct iommufd_vcmdq, obj);
  

• struct iommufd_viommu *viommu = vcmdq->viommu;
• if (viommu->ops->vcmdq_destroy)

• viommu->ops->vcmdq_destroy(vcmdq);
  

• iopt_unpin_pages(&viommu->hwpt->ioas->iopt, vcmdq->addr, vcmdq->length);
• refcount_dec(&viommu->obj.users);

+}

+int iommufd_vcmdq_alloc_ioctl(struct iommufd_ucmd *ucmd) +{

• struct iommu_vcmdq_alloc *cmd = ucmd->cmd;
• struct iommufd_viommu *viommu;
• struct iommufd_vcmdq *vcmdq;
• struct page **pages;
• int max_npages, i;
• dma_addr_t end;
• int rc;
• if (cmd->flags || cmd->type == IOMMU_VCMDQ_TYPE_DEFAULT)

• return -EOPNOTSUPP;
  

The cmd->type check is a little confusing here, I think we could re-order the series and add this check when we have the CMDQV type. Alternatively, we could keep this in place and add the driver-specific vcmdq_alloc op calls when it's added/available for Tegra CMDQV while stubbing out the rest of this function accordingly.

• if (!cmd->addr || !cmd->length)

• return -EINVAL;
  

• if (check_add_overflow(cmd->addr, cmd->length - 1, &end))

• return -EOVERFLOW;
  

• max_npages = DIV_ROUND_UP(cmd->length, PAGE_SIZE);
• pages = kcalloc(max_npages, sizeof(*pages), GFP_KERNEL);
• if (!pages)

• return -ENOMEM;
  

• viommu = iommufd_get_viommu(ucmd, cmd->viommu_id);
• if (IS_ERR(viommu)) {

• rc = PTR_ERR(viommu);
  

• goto out_free;
  

• }
• if (!viommu->ops || !viommu->ops->vcmdq_alloc) {

• rc = -EOPNOTSUPP;
  

• goto out_put_viommu;
  

• }
• /* Quick test on the base address */
• if (!iommu_iova_to_phys(viommu->hwpt->common.domain, cmd->addr)) {

• rc = -ENXIO;
  

• goto out_put_viommu;
  

• }
• /* The underlying physical pages must be pinned in the IOAS */
• rc = iopt_pin_pages(&viommu->hwpt->ioas->iopt, cmd->addr, cmd->length,

• 	    pages, 0);
  

• if (rc)

• goto out_put_viommu;
  

• /* Validate if the underlying physical pages are contiguous */
• for (i = 1; i < max_npages && pages[i]; i++) {

• if (page_to_pfn(pages[i]) == page_to_pfn(pages[i - 1]) + 1)
  

• 	continue;
  

• rc = -EFAULT;
  

• goto out_unpin;
  

• }
• vcmdq = viommu->ops->vcmdq_alloc(viommu, cmd->type, cmd->index,

• 			 cmd->addr, cmd->length);
  

• if (IS_ERR(vcmdq)) {

• rc = PTR_ERR(vcmdq);
  

• goto out_unpin;
  

• }
• vcmdq->viommu = viommu;
• refcount_inc(&viommu->obj.users);
• vcmdq->addr = cmd->addr;
• vcmdq->ictx = ucmd->ictx;
• vcmdq->length = cmd->length;
• cmd->out_vcmdq_id = vcmdq->obj.id;
• rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
• if (rc)

• iommufd_object_abort_and_destroy(ucmd->ictx, &vcmdq->obj);
  

• else

• iommufd_object_finalize(ucmd->ictx, &vcmdq->obj);
  

• goto out_put_viommu;

+out_unpin:

• iopt_unpin_pages(&viommu->hwpt->ioas->iopt, cmd->addr, cmd->length);

+out_put_viommu:

• iommufd_put_object(ucmd->ictx, &viommu->obj);

+out_free:

• kfree(pages);
• return rc;

+}

2.43.0