[PATCH v2 2/2] vhost-vdpa: introduce NO-IOMMU backend feature bit

[Srujana Challa <schalla@xxxxxxxxxxx>]

This patch introduces the VHOST_BACKEND_F_NOIOMMU feature flag.
This flag allows userspace to identify if the driver can operate
without an IOMMU, providing more flexibility in environments where
IOMMU is not available or desired.

Key changes include:
    - Addition of the VHOST_BACKEND_F_NOIOMMU feature flag.
    - Updates to vhost_vdpa_unlocked_ioctl to handle the NO-IOMMU
      feature.
The NO-IOMMU mode is enabled if:
    - The vdpa device lacks an IOMMU domain.
    - The system has the required RAWIO permissions.
    - The vdpa device explicitly supports NO-IOMMU mode.

This feature flag indicates to userspace that the driver can safely
operate in NO-IOMMU mode. If the flag is absent, userspace should
assume NO-IOMMU mode is unsupported and take appropriate actions.

Signed-off-by: Srujana Challa <schalla@xxxxxxxxxxx>
---
 drivers/vhost/vdpa.c             | 11 ++++++++++-
 include/uapi/linux/vhost_types.h |  2 ++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index b3085189ea4a..de47349eceff 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -797,7 +797,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 				 BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST) |
 				 BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
 				 BIT_ULL(VHOST_BACKEND_F_RESUME) |
-				 BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK)))
+				 BIT_ULL(VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK) |
+				 BIT_ULL(VHOST_BACKEND_F_NOIOMMU)))
 			return -EOPNOTSUPP;
 		if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
 		     !vhost_vdpa_can_suspend(v))
@@ -814,6 +815,12 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 		if ((features & BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST)) &&
 		     !vhost_vdpa_has_persistent_map(v))
 			return -EOPNOTSUPP;
+		if ((features & BIT_ULL(VHOST_BACKEND_F_NOIOMMU)) &&
+		    !v->noiommu_en)
+			return -EOPNOTSUPP;
+		if (!(features & BIT_ULL(VHOST_BACKEND_F_NOIOMMU)) &&
+		    v->noiommu_en)
+			return -EOPNOTSUPP;
 		vhost_set_backend_features(&v->vdev, features);
 		return 0;
 	}
@@ -871,6 +878,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
 			features |= BIT_ULL(VHOST_BACKEND_F_DESC_ASID);
 		if (vhost_vdpa_has_persistent_map(v))
 			features |= BIT_ULL(VHOST_BACKEND_F_IOTLB_PERSIST);
+		if (v->noiommu_en)
+			features |= BIT_ULL(VHOST_BACKEND_F_NOIOMMU);
 		features |= vhost_vdpa_get_backend_features(v);
 		if (copy_to_user(featurep, &features, sizeof(features)))
 			r = -EFAULT;
diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
index d7656908f730..dda673c3456a 100644
--- a/include/uapi/linux/vhost_types.h
+++ b/include/uapi/linux/vhost_types.h
@@ -192,5 +192,7 @@ struct vhost_vdpa_iova_range {
 #define VHOST_BACKEND_F_DESC_ASID    0x7
 /* IOTLB don't flush memory mapping across device reset */
 #define VHOST_BACKEND_F_IOTLB_PERSIST  0x8
+/* Enables the device to operate in NO-IOMMU mode as well */
+#define VHOST_BACKEND_F_NOIOMMU  0x9
 
 #endif
-- 
2.25.1