[RFC PATCH v2 08/16] vfio/pci: Gate device information queries and DMA-BUF export

[Shameer Kolothum <skolothumtho@nvidia.com>]

GET_INFO accesses PCI configuration to report AtomicOps support, and
GET_REGION_INFO maps the ROM to validate its contents. Protect these
hardware accesses with access_srcu.

Hold SRCU through DMA-BUF creation and list insertion so recovery cannot
finish revoking buffers before a concurrent export becomes visible.

Assisted-by: LLM
Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
---
 drivers/vfio/pci/vfio_pci_core.c   | 13 ++++++++++++-
 drivers/vfio/pci/vfio_pci_dmabuf.c | 16 +++++++++++++---
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 38551bdedc89..92497224f471 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1112,7 +1112,7 @@ static int vfio_pci_ioctl_get_info(struct vfio_pci_core_device *vdev,
 	unsigned long minsz = offsetofend(struct vfio_device_info, num_irqs);
 	struct vfio_device_info info = {};
 	struct vfio_info_cap caps = { .buf = NULL, .size = 0 };
-	int ret;
+	int ret, idx;
 
 	if (copy_from_user(&info, arg, minsz))
 		return -EFAULT;
@@ -1137,7 +1137,13 @@ static int vfio_pci_ioctl_get_info(struct vfio_pci_core_device *vdev,
 		return ret;
 	}
 
+	idx = vfio_pci_core_access_begin(vdev);
+	if (idx < 0) {
+		kfree(caps.buf);
+		return idx;
+	}
 	ret = vfio_pci_info_atomic_cap(vdev, &caps);
+	vfio_pci_core_access_end(vdev, idx);
 	if (ret && ret != -ENODEV) {
 		pci_warn(vdev->pdev,
 			 "Failed to setup AtomicOps info capability\n");
@@ -1213,6 +1219,10 @@ int vfio_pci_ioctl_get_region_info(struct vfio_device *core_vdev,
 			 * Check ROM content is valid. Need to enable memory
 			 * decode for ROM access in pci_map_rom().
 			 */
+			int idx = vfio_pci_core_access_begin(vdev);
+
+			if (idx < 0)
+				return idx;
 			cmd = vfio_pci_memory_lock_and_enable(vdev);
 			io = pci_map_rom(pdev, &size);
 			if (io) {
@@ -1223,6 +1233,7 @@ int vfio_pci_ioctl_get_region_info(struct vfio_device *core_vdev,
 				pci_unmap_rom(pdev, io);
 			}
 			vfio_pci_memory_unlock_and_restore(vdev, cmd);
+			vfio_pci_core_access_end(vdev, idx);
 		} else if (pdev->rom && pdev->romlen) {
 			info->flags = VFIO_REGION_INFO_FLAG_READ;
 			/* Report BAR size as power of two. */
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index c16f460c01d6..c1a0250af680 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -227,7 +227,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
 	struct vfio_pci_dma_buf *priv;
 	size_t length;
-	int ret;
+	int ret, idx;
 
 	if (!vdev->pci_ops || !vdev->pci_ops->get_dmabuf_phys)
 		return -EOPNOTSUPP;
@@ -274,19 +274,26 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 	priv->vdev = vdev;
 	priv->nr_ranges = get_dma_buf.nr_ranges;
 	priv->size = length;
+
+	idx = vfio_pci_core_access_begin(vdev);
+	if (idx < 0) {
+		ret = idx;
+		goto err_free_phys;
+	}
+
 	ret = vdev->pci_ops->get_dmabuf_phys(vdev, &priv->provider,
 					     get_dma_buf.region_index,
 					     priv->phys_vec, dma_ranges,
 					     priv->nr_ranges);
 	if (ret)
-		goto err_free_phys;
+		goto err_access;
 
 	kfree(dma_ranges);
 	dma_ranges = NULL;
 
 	if (!vfio_device_try_get_registration(&vdev->vdev)) {
 		ret = -ENODEV;
-		goto err_free_phys;
+		goto err_access;
 	}
 
 	exp_info.ops = &vfio_pci_dmabuf_ops;
@@ -311,6 +318,7 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 	list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
 	dma_resv_unlock(priv->dmabuf->resv);
 	up_write(&vdev->memory_lock);
+	vfio_pci_core_access_end(vdev, idx);
 
 	/*
 	 * dma_buf_fd() consumes the reference, when the file closes the dmabuf
@@ -324,6 +332,8 @@ int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 
 err_dev_put:
 	vfio_device_put_registration(&vdev->vdev);
+err_access:
+	vfio_pci_core_access_end(vdev, idx);
 err_free_phys:
 	kfree(priv->phys_vec);
 err_free_priv:
-- 
2.43.0