Re: [PATCH v2 3/3] iommufd/vdevice: add TSM guest request ioctl

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Jason Gunthorpe <jgg@ziepe.ca> writes:

> On Mon, Mar 09, 2026 at 04:47:04PM +0530, Aneesh Kumar K.V (Arm) wrote:
>> +/**
>> + * struct iommu_vdevice_tsm_guest_request - ioctl(IOMMU_VDEVICE_TSM_GUEST_REQUEST)
>> + * @size: sizeof(struct iommu_vdevice_tsm_guest_request)
>> + * @vdevice_id: vDevice ID the guest request is for
>> + * @scope: scope of tsm guest request
>> + * @req_len: the blob size for @req_uptr, filled by guest
>> + * @resp_len: the blob size for @resp_uptr, filled by guest
>> + * @req_uptr: request data buffer filled by guest
>> + * @resp_uptr: response data buffer
>> + */
>
> This needs a much better kdoc.
>
> Refer to specs that define this.
>
> Explain WTF scope is
>
>> +struct iommu_vdevice_tsm_guest_request {
>> +	__u32 size;
>> +	__u32 vdevice_id;
>> +	__u32 scope;
>> +	__u32 req_len;
>> +	__u32 resp_len;
>
> do not leave implicit padding, add a reserved, and check it is 0
>
> Jason
 
How about this change?

modified   drivers/iommu/iommufd/tsm.c
@@ -94,6 +94,9 @@ int iommufd_vdevice_tsm_guest_request_ioctl(struct iommufd_ucmd *ucmd)
 		.resp_len = cmd->resp_len,
 	};
 
+	if (cmd->__reserved)
+		return -EOPNOTSUPP;
+
 	vdev = iommufd_get_vdevice(ucmd->ictx, cmd->vdevice_id);
 	if (IS_ERR(vdev))
 		return PTR_ERR(vdev);
modified   include/uapi/linux/iommufd.h
@@ -1370,11 +1370,27 @@ struct iommu_hw_queue_alloc {
  * struct iommu_vdevice_tsm_guest_request - ioctl(IOMMU_VDEVICE_TSM_GUEST_REQUEST)
  * @size: sizeof(struct iommu_vdevice_tsm_guest_request)
  * @vdevice_id: vDevice ID the guest request is for
- * @scope: scope of tsm guest request
- * @req_len: the blob size for @req_uptr, filled by guest
- * @resp_len: the blob size for @resp_uptr, filled by guest
- * @req_uptr: request data buffer filled by guest
- * @resp_uptr: response data buffer
+ * @scope: Scope classification of the guest request, one of enum
+ *         pci_tsm_req_scope values accepted by pci_tsm_guest_req()
+ * @req_len: Size in bytes of the input payload at @req_uptr
+ * @resp_len: Size in bytes of the output buffer at @resp_uptr
+ * @__reserved: Must be 0
+ * @req_uptr: Userspace pointer to the guest-provided request payload
+ * @resp_uptr: Userspace pointer to the guest response buffer
+ *
+ * Forward a guest request to the TSM bound vDevice. This is intended for
+ * guest TSM/TDISP message transport where the host kernel only marshals
+ * bytes between userspace and the TSM implementation.
+ *
+ * @scope limits requests to TDISP state management, or limited debug.
+ * Requests outside the allowed scope are rejected.
+ *
+ * The request payload is read from @req_uptr/@req_len. If a response is
+ * expected, userspace provides @resp_uptr/@resp_len as writable storage for
+ * response bytes returned by the TSM path.
+ *
+ * The ioctl is only suitable for commands and results that the host kernel
+ * has no use, the host is only facilitating guest to TSM communication.
  */
 struct iommu_vdevice_tsm_guest_request {
 	__u32 size;
@@ -1382,6 +1398,7 @@ struct iommu_vdevice_tsm_guest_request {
 	__u32 scope;
 	__u32 req_len;
 	__u32 resp_len;
+	__u32 __reserved;
 	__aligned_u64 req_uptr;
 	__aligned_u64 resp_uptr;
 };