[PATCH v2 9/9] vfio/pci: Add mmap() attributes to DMABUF feature

[Matt Evans <mattev@meta.com>]

A new VFIO feature, VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR, is added to
set (and get) CPU-facing memory type attributes for a DMABUF exported
from vfio-pci.  These are used for subsequent mmap()s of the buffer.

There are two attributes supported:
 - The default, VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_UC
 - VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC, which results in WC
   PTEs for the DMABUF's BAR region.

Signed-off-by: Matt Evans <mattev@meta.com>
---
 drivers/vfio/pci/vfio_pci_core.c   |  2 +
 drivers/vfio/pci/vfio_pci_dmabuf.c | 70 +++++++++++++++++++++++++++++-
 drivers/vfio/pci/vfio_pci_priv.h   | 12 +++++
 include/uapi/linux/vfio.h          | 27 ++++++++++++
 4 files changed, 110 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 5184b3cac160..e256a925e7ce 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1590,6 +1590,8 @@ int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
 		return vfio_pci_core_feature_token(vdev, flags, arg, argsz);
 	case VFIO_DEVICE_FEATURE_DMA_BUF:
 		return vfio_pci_core_feature_dma_buf(vdev, flags, arg, argsz);
+	case VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR:
+		return vfio_pci_core_feature_dma_buf_memattr(vdev, flags, arg, argsz);
 	default:
 		return -ENOTTY;
 	}
diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
index 3fa14760898f..db8b95ddbe18 100644
--- a/drivers/vfio/pci/vfio_pci_dmabuf.c
+++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
@@ -42,7 +42,10 @@ static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *
 	 * contained within the DMABUF size before calling this.
 	 */
 
-	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+	if (READ_ONCE(priv->memattr) == VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC)
+		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+	else
+		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 
 	/* See comments in vfio_pci_core_mmap() re VM_ALLOW_ANY_UNCACHED. */
@@ -464,6 +467,7 @@ 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;
+	priv->memattr = VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_NC;
 	ret = vdev->pci_ops->get_dmabuf_phys(vdev, &priv->provider,
 					     get_dma_buf.region_index,
 					     priv->phys_vec, dma_ranges,
@@ -731,4 +735,68 @@ int vfio_pci_dma_buf_revoke(struct vfio_pci_core_device *vdev, int dmabuf_fd)
 
 	return ret;
 }
+
+int vfio_pci_core_feature_dma_buf_memattr(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_memattr __user *arg,
+	size_t argsz)
+{
+	struct vfio_device_feature_dma_buf_memattr db_attr;
+	struct vfio_pci_dma_buf *priv;
+	struct dma_buf *dmabuf;
+	int ret;
+
+	if (!vdev->pci_ops || !vdev->pci_ops->get_dmabuf_phys)
+		return -EOPNOTSUPP;
+
+	ret = vfio_check_feature(flags, argsz,
+				 VFIO_DEVICE_FEATURE_GET |
+				 VFIO_DEVICE_FEATURE_SET,
+				 sizeof(db_attr));
+	if (ret != 1)
+		return ret;
+
+	if (copy_from_user(&db_attr, arg, sizeof(db_attr)))
+		return -EFAULT;
+
+	dmabuf = dma_buf_get(db_attr.dmabuf_fd);
+	if (IS_ERR(dmabuf))
+		return PTR_ERR(dmabuf);
+
+	/* Verify DMABUF: see comments in vfio_pci_dma_buf_revoke() */
+	priv = dmabuf->priv;
+	if (dmabuf->ops != &vfio_pci_dmabuf_ops || priv->vdev != vdev) {
+		ret = -ENODEV;
+		goto out_put_buf;
+	}
+
+	ret = 0;
+	scoped_guard(rwsem_write, &vdev->memory_lock) {
+		uint32_t old_attr = priv->memattr;
+
+		if (flags & VFIO_DEVICE_FEATURE_SET) {
+			switch(db_attr.memattr) {
+			case VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_NC:
+			case VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC:
+				priv->memattr = db_attr.memattr;
+				break;
+
+			default:
+				ret = -ENOTSUPP;
+			}
+		}
+		db_attr.memattr = old_attr;
+	}
+
+	if (!ret && (flags & VFIO_DEVICE_FEATURE_GET)) {
+		if (copy_to_user(arg, &db_attr, sizeof(db_attr)))
+			ret = -EFAULT;
+	}
+
+ out_put_buf:
+	dma_buf_put(dmabuf);
+
+	return ret;
+
+}
 #endif /* CONFIG_VFIO_PCI_DMABUF */
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index a1e0f4fcb1dc..8067be45beb0 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -41,6 +41,7 @@ struct vfio_pci_dma_buf {
 	struct kref kref;
 	struct completion comp;
 	unsigned long vma_pgoff_adjust;
+	u32 memattr;
 	enum vfio_pci_dma_buf_status status;
 };
 
@@ -154,6 +155,10 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
 int vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 				  struct vfio_device_feature_dma_buf __user *arg,
 				  size_t argsz);
+int vfio_pci_core_feature_dma_buf_memattr(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_memattr __user *arg,
+	size_t argsz);
 int vfio_pci_dma_buf_revoke(struct vfio_pci_core_device *vdev, int dmabuf_fd);
 #else
 static inline int
@@ -163,6 +168,13 @@ vfio_pci_core_feature_dma_buf(struct vfio_pci_core_device *vdev, u32 flags,
 {
 	return -ENOTTY;
 }
+static inline int vfio_pci_core_feature_dma_buf_memattr(
+	struct vfio_pci_core_device *vdev, u32 flags,
+	struct vfio_device_feature_dma_buf_memattr __user *arg,
+	size_t argsz)
+{
+	return -ENODEV;
+}
 static inline int vfio_pci_dma_buf_revoke(struct vfio_pci_core_device *vdev,
 					  int dmabuf_fd)
 {
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 02366e9f8e16..9b0b68f8a1ef 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1564,6 +1564,33 @@ struct vfio_device_feature_dma_buf {
  */
 #define VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2  12
 
+/**
+ * Given a dma_buf fd previously created by
+ * VFIO_DEVICE_FEATURE_DMA_BUF, GET or SET the memory attribute that
+ * will be used by future mmap()s of that fd.  SETting a new attribute
+ * does not affect existing VMAs.
+ *
+ * The default, if no previous SET has been performed, is NC.
+ *
+ * Return: 0 on success, -1 and errno is set on failure:
+ *
+ *  ENOTSUPP: The given memattr is not supported.
+ *  EBADF, EINVAL: dmabuf_fd is not a DMABUF fd.
+ *  ENODEV: The dmabuf_fd does not match this VFIO device.
+ */
+#define VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR 13
+
+/* Valid memory attributes for the memattr field */
+enum vfio_device_dma_buf_memattr {
+	VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_NC = 0, /* pgprot_noncached */
+	VFIO_DEVICE_FEATURE_DMA_BUF_MEMATTR_WC = 1, /* pgprot_writecombine */
+};
+
+struct vfio_device_feature_dma_buf_memattr {
+	__s32	dmabuf_fd;
+	__u32	memattr;
+};
+
 /* -------- API for Type1 VFIO IOMMU -------- */
 
 /**
-- 
2.47.3