Re: [PATCH v1 2/2] vfio/pci: Allow MMIO regions to be exported through dma-buf

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On 22.04.24 08:30, Vivek Kasireddy wrote:
 From Jason Gunthorpe:
"dma-buf has become a way to safely acquire a handle to non-struct page
memory that can still have lifetime controlled by the exporter. Notably
RDMA can now import dma-buf FDs and build them into MRs which allows for
PCI P2P operations. Extend this to allow vfio-pci to export MMIO memory
from PCI device BARs.

The patch design loosely follows the pattern in commit
db1a8dd916aa ("habanalabs: add support for dma-buf exporter") except this
does not support pinning.

Instead, this implements what, in the past, we've called a revocable
attachment using move. In normal situations the attachment is pinned, as a
BAR does not change physical address. However when the VFIO device is
closed, or a PCI reset is issued, access to the MMIO memory is revoked.

Revoked means that move occurs, but an attempt to immediately re-map the
memory will fail. In the reset case a future move will be triggered when
MMIO access returns. As both close and reset are under userspace control
it is expected that userspace will suspend use of the dma-buf before doing
these operations, the revoke is purely for kernel self-defense against a
hostile userspace."

Following enhancements are made to the original patch:
- Use P2P DMA APIs to create pages (ZONE_DEVICE) instead of DMA addrs
- Add a mmap handler to provide CPU access to the dmabuf
- Add support for creating dmabuf from multiple areas (or ranges)

Original-patch-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
---
  drivers/vfio/pci/Makefile          |   1 +
  drivers/vfio/pci/dma_buf.c         | 348 +++++++++++++++++++++++++++++
  drivers/vfio/pci/vfio_pci_config.c |   8 +-
  drivers/vfio/pci/vfio_pci_core.c   |  28 ++-
  drivers/vfio/pci/vfio_pci_priv.h   |  23 ++
  include/linux/vfio_pci_core.h      |   1 +
  include/uapi/linux/vfio.h          |  25 +++
  7 files changed, 426 insertions(+), 8 deletions(-)
  create mode 100644 drivers/vfio/pci/dma_buf.c

diff --git a/drivers/vfio/pci/Makefile b/drivers/vfio/pci/Makefile
index ce7a61f1d912..b2374856ff62 100644
--- a/drivers/vfio/pci/Makefile
+++ b/drivers/vfio/pci/Makefile
@@ -2,6 +2,7 @@
vfio-pci-core-y := vfio_pci_core.o vfio_pci_intrs.o vfio_pci_rdwr.o vfio_pci_config.o
  vfio-pci-core-$(CONFIG_VFIO_PCI_ZDEV_KVM) += vfio_pci_zdev.o
+vfio-pci-core-$(CONFIG_DMA_SHARED_BUFFER) += dma_buf.o
  obj-$(CONFIG_VFIO_PCI_CORE) += vfio-pci-core.o
vfio-pci-y := vfio_pci.o
diff --git a/drivers/vfio/pci/dma_buf.c b/drivers/vfio/pci/dma_buf.c
new file mode 100644
index 000000000000..7bf00fdee69b
--- /dev/null
+++ b/drivers/vfio/pci/dma_buf.c
@@ -0,0 +1,348 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2022, NVIDIA CORPORATION & AFFILIATES.

Not sure if this Copyright (c) is 2022 or 2024.

Zhu Yanjun

+ */
+#include <linux/dma-buf.h>
+#include <linux/pci-p2pdma.h>
+#include <linux/dma-resv.h>
+
+#include "vfio_pci_priv.h"
+
+MODULE_IMPORT_NS(DMA_BUF);
+
+struct vfio_pci_dma_buf {
+	struct dma_buf *dmabuf;
+	struct vfio_pci_core_device *vdev;
+	struct list_head dmabufs_elm;
+	struct page **pages;
+	struct sg_table *sg;
+	unsigned int nr_pages;
+	bool revoked;
+};
+
+static vm_fault_t vfio_pci_dma_buf_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct vfio_pci_dma_buf *priv = vma->vm_private_data;
+	pgoff_t pgoff = vmf->pgoff;
+
+	if (pgoff >= priv->nr_pages)
+		return VM_FAULT_SIGBUS;
+
+	return vmf_insert_pfn(vma, vmf->address,
+			      page_to_pfn(priv->pages[pgoff]));
+}
+
+static const struct vm_operations_struct vfio_pci_dma_buf_vmops = {
+	.fault = vfio_pci_dma_buf_fault,
+};
+
+static int vfio_pci_dma_buf_mmap(struct dma_buf *dmabuf,
+				 struct vm_area_struct *vma)
+{
+	struct vfio_pci_dma_buf *priv = dmabuf->priv;
+
+	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
+		return -EINVAL;
+
+	vma->vm_ops = &vfio_pci_dma_buf_vmops;
+	vma->vm_private_data = priv;
+	vm_flags_set(vma, VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
+	return 0;
+}
+
+static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
+				   struct dma_buf_attachment *attachment)
+{
+	struct vfio_pci_dma_buf *priv = dmabuf->priv;
+	int rc;
+
+	rc = pci_p2pdma_distance_many(priv->vdev->pdev, &attachment->dev, 1,
+				      true);
+	if (rc < 0)
+		attachment->peer2peer = false;
+	return 0;
+}
+
+static void vfio_pci_dma_buf_unpin(struct dma_buf_attachment *attachment)
+{
+}
+
+static int vfio_pci_dma_buf_pin(struct dma_buf_attachment *attachment)
+{
+	/*
+	 * Uses the dynamic interface but must always allow for
+	 * dma_buf_move_notify() to do revoke
+	 */
+	return -EINVAL;
+}
+
+static struct sg_table *
+vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment,
+		     enum dma_data_direction dir)
+{
+	struct vfio_pci_dma_buf *priv = attachment->dmabuf->priv;
+	struct scatterlist *sgl;
+	struct sg_table *sgt;
+	unsigned int i = 0;
+	int ret;
+
+	dma_resv_assert_held(priv->dmabuf->resv);
+
+	if (!attachment->peer2peer)
+		return ERR_PTR(-EPERM);
+
+	if (priv->revoked)
+		return ERR_PTR(-ENODEV);
+
+	sgt = kzalloc(sizeof(*sgt), GFP_KERNEL);
+	if (!sgt)
+		return ERR_PTR(-ENOMEM);
+
+	ret = sg_alloc_table(sgt, priv->nr_pages, GFP_KERNEL);
+	if (ret)
+		goto err_kfree_sgt;
+
+	for_each_sg(sgt->sgl, sgl, priv->nr_pages, i)
+		sg_set_page(sgl, priv->pages[i], PAGE_SIZE, 0);
+
+	ret = dma_map_sgtable(attachment->dev, sgt, dir, 0);
+	if (ret < 0)
+		goto err_free_sgt;
+
+	return sgt;
+
+err_free_sgt:
+	sg_free_table(sgt);
+err_kfree_sgt:
+	kfree(sgt);
+	return ERR_PTR(ret);
+}
+
+static void vfio_pci_dma_buf_unmap(struct dma_buf_attachment *attachment,
+				   struct sg_table *sgt,
+				   enum dma_data_direction dir)
+{
+	dma_unmap_sgtable(attachment->dev, sgt, dir, 0);
+	sg_free_table(sgt);
+	kfree(sgt);
+}
+
+static void release_p2p_pages(struct vfio_pci_dma_buf *priv,
+			      unsigned int nr_pages)
+{
+	while (nr_pages > 0 && priv->pages[--nr_pages])
+		pci_free_p2pmem(priv->vdev->pdev,
+				page_to_virt(priv->pages[nr_pages]),
+				PAGE_SIZE);
+}
+
+static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
+{
+	struct vfio_pci_dma_buf *priv = dmabuf->priv;
+
+	/*
+	 * Either this or vfio_pci_dma_buf_cleanup() will remove from the list.
+	 * The refcount prevents both.
+	 */
+	if (priv->vdev) {
+		release_p2p_pages(priv, priv->nr_pages);
+		kfree(priv->pages);
+		down_write(&priv->vdev->memory_lock);
+		list_del_init(&priv->dmabufs_elm);
+		up_write(&priv->vdev->memory_lock);
+		vfio_device_put_registration(&priv->vdev->vdev);
+	}
+	kfree(priv);
+}
+
+static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
+	.attach = vfio_pci_dma_buf_attach,
+	.map_dma_buf = vfio_pci_dma_buf_map,
+	.pin = vfio_pci_dma_buf_pin,
+	.unpin = vfio_pci_dma_buf_unpin,
+	.release = vfio_pci_dma_buf_release,
+	.unmap_dma_buf = vfio_pci_dma_buf_unmap,
+	.mmap = vfio_pci_dma_buf_mmap,
+};
+
+static int create_p2p_pages(struct vfio_pci_dma_buf *priv, uint32_t nr_areas,
+			    struct vfio_region_p2p_area *p2p_areas)
+{
+	struct pci_dev *pdev = priv->vdev->pdev;
+	resource_size_t bar_size;
+	unsigned int pg = 0;
+	void *vaddr;
+	size_t size;
+	int i, ret;
+
+	for (i = 0; i < nr_areas; i++) {
+		bar_size = pci_resource_len(pdev, p2p_areas[i].region_index);
+		if (p2p_areas[i].offset > bar_size ||
+		    p2p_areas[i].offset + p2p_areas[i].length > bar_size) {
+			ret = -ERANGE;
+			goto err;
+		}
+
+		ret = pci_p2pdma_add_resource(pdev,
+					      p2p_areas[i].region_index,
+					      p2p_areas[i].length,
+					      p2p_areas[i].offset);
+		if (ret)
+			goto err;
+
+		vaddr = pci_alloc_p2pmem(pdev, p2p_areas[i].length);
+		if (!vaddr) {
+			ret = -EINVAL;
+			goto err;
+		}
+
+		for (size = 0; size < p2p_areas[i].length;) {
+			priv->pages[pg++] = virt_to_page(vaddr + size);
+			size += PAGE_SIZE;
+		}
+	}
+
+	return 0;
+
+err:
+	release_p2p_pages(priv, pg);
+	return ret;
+}
+
+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)
+{
+	struct vfio_device_feature_dma_buf get_dma_buf;
+	struct vfio_region_p2p_area *p2p_areas;
+	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct vfio_pci_dma_buf *priv;
+	int i, ret;
+
+	ret = vfio_check_feature(flags, argsz, VFIO_DEVICE_FEATURE_GET,
+				 sizeof(get_dma_buf));
+	if (ret != 1)
+		return ret;
+
+	if (copy_from_user(&get_dma_buf, arg, sizeof(get_dma_buf)))
+		return -EFAULT;
+
+	p2p_areas = memdup_array_user(&arg->p2p_areas,
+				      get_dma_buf.nr_areas,
+				      sizeof(*p2p_areas));
+	if (IS_ERR(p2p_areas))
+		return PTR_ERR(p2p_areas);
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	ret = -ERANGE;
+	for (i = 0; i < get_dma_buf.nr_areas; i++) {
+		/*
+		 * For PCI the region_index is the BAR number like
+		 * everything else.
+		 */
+		if (p2p_areas[i].region_index >= VFIO_PCI_ROM_REGION_INDEX) {
+			goto err_free_priv;
+		}
+
+		if (!IS_ALIGNED(p2p_areas[i].offset, PAGE_SIZE) ||
+		    !IS_ALIGNED(p2p_areas[i].length, PAGE_SIZE))
+			goto err_free_priv;
+
+		priv->nr_pages += p2p_areas[i].length >> PAGE_SHIFT;
+	}
+
+	if (!priv->nr_pages)
+		goto err_free_priv;
+
+	priv->pages = kmalloc_array(priv->nr_pages,
+				    sizeof(*priv->pages), GFP_KERNEL);
+	if (!priv->pages) {
+		ret = -ENOMEM;
+		goto err_free_priv;
+	}
+
+	priv->vdev = vdev;
+	ret = create_p2p_pages(priv, get_dma_buf.nr_areas, p2p_areas);
+	if (ret)
+		goto err_free_priv;
+
+	exp_info.ops = &vfio_pci_dmabuf_ops;
+	exp_info.size = priv->nr_pages << PAGE_SHIFT;
+	exp_info.flags = get_dma_buf.open_flags;
+	exp_info.priv = priv;
+
+	priv->dmabuf = dma_buf_export(&exp_info);
+	if (IS_ERR(priv->dmabuf)) {
+		ret = PTR_ERR(priv->dmabuf);
+		goto err_free_pages;
+	}
+
+	/* dma_buf_put() now frees priv */
+	INIT_LIST_HEAD(&priv->dmabufs_elm);
+	down_write(&vdev->memory_lock);
+	dma_resv_lock(priv->dmabuf->resv, NULL);
+	priv->revoked = !__vfio_pci_memory_enabled(vdev);
+	vfio_device_try_get_registration(&vdev->vdev);
+	list_add_tail(&priv->dmabufs_elm, &vdev->dmabufs);
+	dma_resv_unlock(priv->dmabuf->resv);
+	up_write(&vdev->memory_lock);
+	kfree(p2p_areas);
+
+	/*
+	 * dma_buf_fd() consumes the reference, when the file closes the dmabuf
+	 * will be released.
+	 */
+	return dma_buf_fd(priv->dmabuf, get_dma_buf.open_flags);
+
+err_free_pages:
+	release_p2p_pages(priv, priv->nr_pages);
+err_free_priv:
+	kfree(p2p_areas);
+	kfree(priv->pages);
+	kfree(priv);
+	return ret;
+}
+
+void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
+{
+	struct vfio_pci_dma_buf *priv;
+	struct vfio_pci_dma_buf *tmp;
+
+	lockdep_assert_held_write(&vdev->memory_lock);
+
+	list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
+		if (!get_file_rcu(&priv->dmabuf->file))
+			continue;
+		if (priv->revoked != revoked) {
+			dma_resv_lock(priv->dmabuf->resv, NULL);
+			priv->revoked = revoked;
+			dma_buf_move_notify(priv->dmabuf);
+			dma_resv_unlock(priv->dmabuf->resv);
+		}
+		dma_buf_put(priv->dmabuf);
+	}
+}
+
+void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
+{
+	struct vfio_pci_dma_buf *priv;
+	struct vfio_pci_dma_buf *tmp;
+
+	down_write(&vdev->memory_lock);
+	list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
+		if (!get_file_rcu(&priv->dmabuf->file))
+			continue;
+		dma_resv_lock(priv->dmabuf->resv, NULL);
+		list_del_init(&priv->dmabufs_elm);
+		priv->vdev = NULL;
+		priv->revoked = true;
+		dma_buf_move_notify(priv->dmabuf);
+		dma_resv_unlock(priv->dmabuf->resv);
+		vfio_device_put_registration(&vdev->vdev);
+		dma_buf_put(priv->dmabuf);
+	}
+	up_write(&vdev->memory_lock);
+}
diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index 97422aafaa7b..c605c5cb0078 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -585,10 +585,12 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
  		virt_mem = !!(le16_to_cpu(*virt_cmd) & PCI_COMMAND_MEMORY);
  		new_mem = !!(new_cmd & PCI_COMMAND_MEMORY);
- if (!new_mem)
+		if (!new_mem) {
  			vfio_pci_zap_and_down_write_memory_lock(vdev);
-		else
+			vfio_pci_dma_buf_move(vdev, true);
+		} else {
  			down_write(&vdev->memory_lock);
+		}
/*
  		 * If the user is writing mem/io enable (new_mem/io) and we
@@ -623,6 +625,8 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
  		*virt_cmd &= cpu_to_le16(~mask);
  		*virt_cmd |= cpu_to_le16(new_cmd & mask);
+ if (__vfio_pci_memory_enabled(vdev))
+			vfio_pci_dma_buf_move(vdev, false);
  		up_write(&vdev->memory_lock);
  	}
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index d94d61b92c1a..d2ef982bdb3e 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -700,6 +700,8 @@ void vfio_pci_core_close_device(struct vfio_device *core_vdev)
  #endif
  	vfio_pci_core_disable(vdev);
+ vfio_pci_dma_buf_cleanup(vdev);
+
  	mutex_lock(&vdev->igate);
  	if (vdev->err_trigger) {
  		eventfd_ctx_put(vdev->err_trigger);
@@ -1246,7 +1248,10 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
  	 */
  	vfio_pci_set_power_state(vdev, PCI_D0);
+ vfio_pci_dma_buf_move(vdev, true);
  	ret = pci_try_reset_function(vdev->pdev);
+	if (__vfio_pci_memory_enabled(vdev))
+		vfio_pci_dma_buf_move(vdev, false);
  	up_write(&vdev->memory_lock);
return ret;
@@ -1467,11 +1472,10 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
  }
  EXPORT_SYMBOL_GPL(vfio_pci_core_ioctl);
-static int vfio_pci_core_feature_token(struct vfio_device *device, u32 flags,
-				       uuid_t __user *arg, size_t argsz)
+static int vfio_pci_core_feature_token(struct vfio_pci_core_device *vdev,
+				       u32 flags, uuid_t __user *arg,
+				       size_t argsz)
  {
-	struct vfio_pci_core_device *vdev =
-		container_of(device, struct vfio_pci_core_device, vdev);
  	uuid_t uuid;
  	int ret;
@@ -1498,6 +1502,9 @@ static int vfio_pci_core_feature_token(struct vfio_device *device, u32 flags,
  int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
  				void __user *arg, size_t argsz)
  {
+	struct vfio_pci_core_device *vdev =
+			container_of(device, struct vfio_pci_core_device, vdev);
+
  	switch (flags & VFIO_DEVICE_FEATURE_MASK) {
  	case VFIO_DEVICE_FEATURE_LOW_POWER_ENTRY:
  		return vfio_pci_core_pm_entry(device, flags, arg, argsz);
@@ -1507,7 +1514,9 @@ int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
  	case VFIO_DEVICE_FEATURE_LOW_POWER_EXIT:
  		return vfio_pci_core_pm_exit(device, flags, arg, argsz);
  	case VFIO_DEVICE_FEATURE_PCI_VF_TOKEN:
-		return vfio_pci_core_feature_token(device, flags, arg, argsz);
+		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);
  	default:
  		return -ENOTTY;
  	}
@@ -2182,6 +2191,7 @@ int vfio_pci_core_init_dev(struct vfio_device *core_vdev)
  	mutex_init(&vdev->vma_lock);
  	INIT_LIST_HEAD(&vdev->vma_list);
  	INIT_LIST_HEAD(&vdev->sriov_pfs_item);
+	INIT_LIST_HEAD(&vdev->dmabufs);
  	init_rwsem(&vdev->memory_lock);
  	xa_init(&vdev->ctx);
@@ -2576,11 +2586,17 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
  	 * cause the PCI config space reset without restoring the original
  	 * state (saved locally in 'vdev->pm_save').
  	 */
-	list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list)
+	list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
+		vfio_pci_dma_buf_move(cur, true);
  		vfio_pci_set_power_state(cur, PCI_D0);
+	}
ret = pci_reset_bus(pdev); + list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list)
+		if (__vfio_pci_memory_enabled(cur))
+			vfio_pci_dma_buf_move(cur, false);
+
  err_undo:
  	list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
  		if (cur == cur_mem)
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 5e4fa69aee16..09d3c300918c 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -101,4 +101,27 @@ static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
  	return (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
  }
+#ifdef CONFIG_DMA_SHARED_BUFFER
+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);
+void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev);
+void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked);
+#else
+static 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)
+{
+	return -ENOTTY;
+}
+static inline void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
+{
+}
+static inline void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev,
+					 bool revoked)
+{
+}
+#endif
+
  #endif
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index a2c8b8bba711..387cce561dad 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -96,6 +96,7 @@ struct vfio_pci_core_device {
  	struct mutex		vma_lock;
  	struct list_head	vma_list;
  	struct rw_semaphore	memory_lock;
+	struct list_head	dmabufs;
  };
/* Will be exported for vfio pci drivers usage */
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 2b68e6cdf190..47d230c5df25 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1458,6 +1458,31 @@ struct vfio_device_feature_bus_master {
  };
  #define VFIO_DEVICE_FEATURE_BUS_MASTER 10
+/**
+ * Upon VFIO_DEVICE_FEATURE_GET create a dma_buf fd for the
+ * region selected.
+ *
+ * open_flags are the typical flags passed to open(2), eg O_RDWR, O_CLOEXEC,
+ * etc. offset/length specify a slice of the region to create the dmabuf from.
+ * If both are 0 then the whole region is used.
+ *
+ * Return: The fd number on success, -1 and errno is set on failure.
+ */
+#define VFIO_DEVICE_FEATURE_DMA_BUF 11
+
+struct vfio_region_p2p_area {
+	__u32	region_index;
+	__u32	__pad;
+	__u64	offset;
+	__u64	length;
+};
+
+struct vfio_device_feature_dma_buf {
+	__u32	open_flags;
+	__u32	nr_areas;
+	struct vfio_region_p2p_area p2p_areas[];
+};
+
  /* -------- API for Type1 VFIO IOMMU -------- */
/**




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