[RFC PATCH 05/10] vfio: Create a vfio_device from vma lookup

[Alex Williamson <alex.williamson@xxxxxxxxxx>]

Introduce a vfio bus driver policy where using the exported
vfio_device_vma_open() as the vm_ops.open for a vma indicates
vm_private_data is the struct vfio_device pointer associated
to the vma.  This allows a direct vma to device lookup.

Operating on an active, open vma to the device, we should be
able to directly increment the vfio_device reference.

Implemented only for vfio-pci for now.

Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
---
 drivers/vfio/pci/vfio_pci.c |    6 ++++--
 drivers/vfio/vfio.c         |   24 ++++++++++++++++++++++++
 include/linux/vfio.h        |    2 ++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 115f10f7b096..f9529bac6c97 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -1469,7 +1469,8 @@ void vfio_pci_memory_unlock_and_restore(struct vfio_pci_device *vdev, u16 cmd)
 static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
-	struct vfio_pci_device *vdev = vma->vm_private_data;
+	struct vfio_device *device = vma->vm_private_data;
+	struct vfio_pci_device *vdev = vfio_device_data(device);
 	vm_fault_t ret = VM_FAULT_SIGBUS;
 
 	down_read(&vdev->memory_lock);
@@ -1485,6 +1486,7 @@ static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf)
 }
 
 static const struct vm_operations_struct vfio_pci_mmap_ops = {
+	.open = vfio_device_vma_open,
 	.fault = vfio_pci_mmap_fault,
 };
 
@@ -1542,7 +1544,7 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma)
 		}
 	}
 
-	vma->vm_private_data = vdev;
+	vma->vm_private_data = vdev->device;
 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	vma->vm_pgoff = (pci_resource_start(pdev, index) >> PAGE_SHIFT) + pgoff;
 
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index da212425ab30..399c42b77fbb 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -572,6 +572,15 @@ void vfio_device_unmap_mapping_range(struct vfio_device *device,
 }
 EXPORT_SYMBOL_GPL(vfio_device_unmap_mapping_range);
 
+/*
+ * A VFIO bus driver using this open callback will provide a
+ * struct vfio_device pointer in the vm_private_data field.
+ */
+void vfio_device_vma_open(struct vm_area_struct *vma)
+{
+}
+EXPORT_SYMBOL_GPL(vfio_device_vma_open);
+
 /**
  * Device objects - create, release, get, put, search
  */
@@ -927,6 +936,21 @@ struct vfio_device *vfio_device_get_from_dev(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(vfio_device_get_from_dev);
 
+struct vfio_device *vfio_device_get_from_vma(struct vm_area_struct *vma)
+{
+	struct vfio_device *device;
+
+	if (vma->vm_ops->open != vfio_device_vma_open)
+		return ERR_PTR(-ENODEV);
+
+	device = vma->vm_private_data;
+
+	vfio_device_get(device);
+
+	return device;
+}
+EXPORT_SYMBOL_GPL(vfio_device_get_from_vma);
+
 static struct vfio_device *vfio_device_get_from_name(struct vfio_group *group,
 						     char *buf)
 {
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index f435dfca15eb..188c2f3feed9 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -58,6 +58,8 @@ extern void vfio_device_put(struct vfio_device *device);
 extern void *vfio_device_data(struct vfio_device *device);
 extern void vfio_device_unmap_mapping_range(struct vfio_device *device,
 					    loff_t start, loff_t len);
+extern void vfio_device_vma_open(struct vm_area_struct *vma);
+extern struct vfio_device *vfio_device_get_from_vma(struct vm_area_struct *vma);
 
 /* events for the backend driver notify callback */
 enum vfio_iommu_notify_type {