[RFC][PATCH v2 02/13] vfio: add VFIO_IOMMU_GET_VMID and VFIO_IOMMU_SET_VMID

[Nicolin Chen <nicolinc@nvidia.com>]

This patch adds a pair of new ioctl commands to communicate with
user space (virtual machine hypervisor) to get and set VMID that
indicates a Virtual Machine Identifier, being used by some IOMMU
to tag TLB entries -- similar to CPU MMU, using this VMID number
allows IOMMU to invalidate at the same time TLBs of the same VM.

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 drivers/vfio/vfio.c       | 13 +++++++++++++
 include/uapi/linux/vfio.h | 26 ++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 3c034fe14ccb..c17b25c127a2 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -59,6 +59,7 @@ struct vfio_container {
 	struct rw_semaphore		group_lock;
 	struct vfio_iommu_driver	*iommu_driver;
 	void				*iommu_data;
+	u32				vmid;
 	bool				noiommu;
 };
 
@@ -1190,6 +1191,16 @@ static long vfio_fops_unl_ioctl(struct file *filep,
 	case VFIO_SET_IOMMU:
 		ret = vfio_ioctl_set_iommu(container, arg);
 		break;
+	case VFIO_IOMMU_GET_VMID:
+		ret = copy_to_user((void __user *)arg, &container->vmid,
+				   sizeof(u32)) ? -EFAULT : 0;
+		break;
+	case VFIO_IOMMU_SET_VMID:
+		if ((u32)arg == VFIO_IOMMU_VMID_INVALID)
+			return -EINVAL;
+		container->vmid = (u32)arg;
+		ret = 0;
+		break;
 	default:
 		driver = container->iommu_driver;
 		data = container->iommu_data;
@@ -1213,6 +1224,8 @@ static int vfio_fops_open(struct inode *inode, struct file *filep)
 	init_rwsem(&container->group_lock);
 	kref_init(&container->kref);
 
+	container->vmid = VFIO_IOMMU_VMID_INVALID;
+
 	filep->private_data = container;
 
 	return 0;
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index ef33ea002b0b..58c5fa6aaca6 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1216,6 +1216,32 @@ struct vfio_iommu_type1_dirty_bitmap_get {
 
 #define VFIO_IOMMU_DIRTY_PAGES             _IO(VFIO_TYPE, VFIO_BASE + 17)
 
+/**
+ * VFIO_IOMMU_GET_VMID - _IOWR(VFIO_TYPE, VFIO_BASE + 22, __u32 *vmid)
+ * VFIO_IOMMU_SET_VMID - _IOWR(VFIO_TYPE, VFIO_BASE + 23, __u32 vmid)
+ *
+ * IOCTLs are used for VMID alignment between Kernel and User Space hypervisor.
+ * In a virtualization use case, a guest owns the first stage translation, and
+ * the hypervisor owns the second stage translation. VMID is an Virtual Machine
+ * Identifier that is to tag TLB entries of a VM. If a VM has multiple physical
+ * devices being assigned to it, while these devices are under different IOMMU
+ * domains, the VMIDs in the second stage configurations of these IOMMU domains
+ * could be aligned to a unified VMID value. This could be achieved by using
+ * these two IOCTLs.
+ *
+ * Caller should get VMID upon its initial value when the first physical device
+ * is assigned to the VM.
+ *
+ * Caller then should set VMID to share the same VMID value with other physical
+ * devices being assigned to the same VM.
+ *
+ */
+#define VFIO_IOMMU_VMID_INVALID		(-1U)
+
+#define VFIO_IOMMU_GET_VMID		_IO(VFIO_TYPE, VFIO_BASE + 22)
+
+#define VFIO_IOMMU_SET_VMID		_IO(VFIO_TYPE, VFIO_BASE + 23)
+
 /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
 
 /*
-- 
2.17.1