iommufd: Make vfio_compat's unmap succeed if the range is already empty

iommufd returns ENOENT when attempting to unmap a range that is already
empty, while vfio type1 returns success. Fix vfio_compat to match.

Fixes: d624d66 ("iommufd: vfio container FD ioctl compatibility")
Link: https://patch.msgid.link/r/[email protected]
Reviewed-by: Nicolin Chen <[email protected]>
Reviewed-by: Alex Mastro <[email protected]>
Reported-by: Alex Mastro <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jason Gunthorpe <[email protected]>

Author: jgunthorpe

drivers/iommu/iommufd/io_pagetable.c

@@ -707,7 +707,8 @@ static int iopt_unmap_iova_range(struct io_pagetable *iopt, unsigned long start,
 	struct iopt_area *area;
 	unsigned long unmapped_bytes = 0;
 	unsigned int tries = 0;
-	int rc = -ENOENT;
+	/* If there are no mapped entries then success */
+	int rc = 0;
 
 	/*
 	 * The domains_rwsem must be held in read mode any time any area->pages
@@ -777,8 +778,6 @@ static int iopt_unmap_iova_range(struct io_pagetable *iopt, unsigned long start,
 
 		down_write(&iopt->iova_rwsem);
 	}
-	if (unmapped_bytes)
-		rc = 0;
 
 out_unlock_iova:
 	up_write(&iopt->iova_rwsem);
@@ -815,13 +814,8 @@ int iopt_unmap_iova(struct io_pagetable *iopt, unsigned long iova,
 
 int iopt_unmap_all(struct io_pagetable *iopt, unsigned long *unmapped)
 {
-	int rc;
-
-	rc = iopt_unmap_iova_range(iopt, 0, ULONG_MAX, unmapped);
 	/* If the IOVAs are empty then unmap all succeeds */
-	if (rc == -ENOENT)
-		return 0;
-	return rc;
+	return iopt_unmap_iova_range(iopt, 0, ULONG_MAX, unmapped);
 }
 
 /* The caller must always free all the nodes in the allowed_iova rb_root. */

drivers/iommu/iommufd/ioas.c

@@ -367,6 +367,10 @@ int iommufd_ioas_unmap(struct iommufd_ucmd *ucmd)
 				     &unmapped);
 		if (rc)
 			goto out_put;
+		if (!unmapped) {
+			rc = -ENOENT;
+			goto out_put;
+		}
 	}
 
 	cmd->length = unmapped;

tools/testing/selftests/iommu/iommufd.c

@@ -2638,6 +2638,8 @@ TEST_F(vfio_compat_mock_domain, map)
 	ASSERT_EQ(0, ioctl(self->fd, VFIO_IOMMU_MAP_DMA, &map_cmd));
 	ASSERT_EQ(0, ioctl(self->fd, VFIO_IOMMU_UNMAP_DMA, &unmap_cmd));
 	ASSERT_EQ(BUFFER_SIZE, unmap_cmd.size);
+	/* Unmap of empty is success */
+	ASSERT_EQ(0, ioctl(self->fd, VFIO_IOMMU_UNMAP_DMA, &unmap_cmd));
 
 	/* UNMAP_FLAG_ALL requires 0 iova/size */
 	ASSERT_EQ(0, ioctl(self->fd, VFIO_IOMMU_MAP_DMA, &map_cmd));