[RFC PATCH 2/3] iommufd/viommu: Add support to associate viommu with kvm instance

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

The associated kvm instance will be used in later patch by iommufd to
bind a tdi to kvm.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 drivers/iommu/iommufd/viommu.c | 48 ++++++++++++++++++++++++++++++++--
 include/linux/iommufd.h        |  3 +++
 include/uapi/linux/iommufd.h   |  2 ++
 3 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommufd/viommu.c b/drivers/iommu/iommufd/viommu.c
index 01df2b985f02..10d343871fb2 100644
--- a/drivers/iommu/iommufd/viommu.c
+++ b/drivers/iommu/iommufd/viommu.c
@@ -2,6 +2,37 @@
 /* Copyright (c) 2024, NVIDIA CORPORATION & AFFILIATES
  */
 #include "iommufd_private.h"
+#include "linux/tsm.h"
+
+#if IS_ENABLED(CONFIG_KVM)
+#include <linux/kvm_host.h>
+
+static int viommu_get_kvm(struct iommufd_viommu *viommu, int kvm_vm_fd)
+{
+	int rc = -EBADF;
+	struct kvm *kvm;
+	struct fd f = fdget(kvm_vm_fd);
+
+	if (!fd_file(f) || !file_is_kvm(fd_file(f)))
+		goto err_out;
+
+	kvm = fd_file(f)->private_data;
+	if (!kvm)
+		goto err_out;
+
+	/* hold the kvm reference via file descriptor */
+	viommu->kvm_fd = f;
+	return rc;
+err_out:
+	fdput(f);
+	return rc;
+}
+
+static void viommu_put_kvm(struct iommufd_viommu *viommu)
+{
+	fdput(viommu->kvm_fd);
+}
+#endif
 
 void iommufd_viommu_destroy(struct iommufd_object *obj)
 {
@@ -12,6 +43,8 @@ void iommufd_viommu_destroy(struct iommufd_object *obj)
 		viommu->ops->destroy(viommu);
 	refcount_dec(&viommu->hwpt->common.obj.users);
 	xa_destroy(&viommu->vdevs);
+
+	viommu_put_kvm(viommu);
 }
 
 int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd)
@@ -23,7 +56,9 @@ int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd)
 	const struct iommu_ops *ops;
 	int rc;
 
-	if (cmd->flags || cmd->type == IOMMU_VIOMMU_TYPE_DEFAULT)
+	if (cmd->flags & ~IOMMU_VIOMMU_KVM_FD)
+		return -EOPNOTSUPP;
+	if (cmd->type == IOMMU_VIOMMU_TYPE_DEFAULT)
 		return -EOPNOTSUPP;
 
 	idev = iommufd_get_device(ucmd, cmd->dev_id);
@@ -68,10 +103,19 @@ int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd)
 	 */
 	viommu->iommu_dev = __iommu_get_iommu_dev(idev->dev);
 
+	/* get the kvm details if specified. */
+	if (cmd->flags & IOMMU_VIOMMU_KVM_FD) {
+		rc = viommu_get_kvm(viommu, cmd->kvm_vm_fd);
+		if (rc)
+			goto out_abort;
+	}
+
 	cmd->out_viommu_id = viommu->obj.id;
 	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
-	if (rc)
+	if (rc) {
+		viommu_put_kvm(viommu);
 		goto out_abort;
+	}
 	iommufd_object_finalize(ucmd->ictx, &viommu->obj);
 	goto out_put_hwpt;
 
diff --git a/include/linux/iommufd.h b/include/linux/iommufd.h
index 34b6e6ca4bfa..ed5c404f1b0b 100644
--- a/include/linux/iommufd.h
+++ b/include/linux/iommufd.h
@@ -12,6 +12,7 @@
 #include <linux/refcount.h>
 #include <linux/types.h>
 #include <linux/xarray.h>
+#include <linux/file.h>
 #include <uapi/linux/iommufd.h>
 
 struct device;
@@ -51,6 +52,7 @@ struct iommufd_object {
 	unsigned int id;
 };
 
+struct kvm;
 struct iommufd_device *iommufd_device_bind(struct iommufd_ctx *ictx,
 					   struct device *dev, u32 *id);
 void iommufd_device_unbind(struct iommufd_device *idev);
@@ -94,6 +96,7 @@ struct iommufd_viommu {
 	struct iommufd_ctx *ictx;
 	struct iommu_device *iommu_dev;
 	struct iommufd_hwpt_paging *hwpt;
+	struct fd kvm_fd;
 
 	const struct iommufd_viommu_ops *ops;
 
diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
index f29b6c44655e..b3b962d857c7 100644
--- a/include/uapi/linux/iommufd.h
+++ b/include/uapi/linux/iommufd.h
@@ -957,6 +957,7 @@ enum iommu_viommu_type {
 	IOMMU_VIOMMU_TYPE_ARM_SMMUV3 = 1,
 };
 
+#define IOMMU_VIOMMU_KVM_FD	BIT(0)
 /**
  * struct iommu_viommu_alloc - ioctl(IOMMU_VIOMMU_ALLOC)
  * @size: sizeof(struct iommu_viommu_alloc)
@@ -985,6 +986,7 @@ struct iommu_viommu_alloc {
 	__u32 dev_id;
 	__u32 hwpt_id;
 	__u32 out_viommu_id;
+	__u32 kvm_vm_fd;
 };
 #define IOMMU_VIOMMU_ALLOC _IO(IOMMUFD_TYPE, IOMMUFD_CMD_VIOMMU_ALLOC)
 
-- 
2.43.0