[PATCH v5 0/3] AER-KVM: Error containment of VFIO devices assigned to KVM guests

[PATCH v5 0/3] AER-KVM: Error containment of VFIO devices assigned to KVM guests

[Vijay Mohan Pandarathil]

Add support for error containment when a VFIO device assigned to a KVM
guest encounters an error. This is for PCIe devices/drivers that support AER
functionality. When the host OS is notified of an error in a device either
through the firmware first approach or through an interrupt handled by the AER
root port driver, the error handler registered by the vfio-pci driver gets
invoked. The qemu process is signaled through an eventfd registered per
VFIO device by the qemu process. In the eventfd handler, qemu decides on
what action to take. In this implementation, guest is brought down to
contain the error.


v5:
 - Rebased to latest upstream stable bits
 - Incorporated v4 feedback
v4:
 - Stop the guest instead of terminating
 - Remove unwanted returns from functions
 - Incorporate other feedback
v3:
 - Removed PCI_AER* flags from device info ioctl.
 - Incorporated feedback
v2:
 - Rebased to latest upstream stable bits
 - Changed the new ioctl to be part of VFIO_SET_IRQs ioctl
 - Added a new patch to get/put reference to a vfio device from struct device
 - Incorporated all other feedback.

---

Vijay Mohan Pandarathil(3):

[PATCH 1/3] VFIO: Wrapper to get reference to vfio_device from device 
[PATCH 2/3] VFIO-AER: Vfio-pci driver changes for supporting AER
[PATCH 3/3] QEMU-AER: Qemu changes to support AER for VFIO-PCI devices

Kernel files changed

 drivers/vfio/vfio.c  | 47 ++++++++++++++++++++++++++++++++++-------------
 include/linux/vfio.h |  3 +++
 2 files changed, 37 insertions(+), 13 deletions(-)

 drivers/vfio/pci/vfio_pci.c         | 44 ++++++++++++++++++++++++++++++++-
 drivers/vfio/pci/vfio_pci_intrs.c   | 49 +++++++++++++++++++++++++++++++++++++
 drivers/vfio/pci/vfio_pci_private.h |  1 +
 include/uapi/linux/vfio.h           |  1 +
 4 files changed, 94 insertions(+), 1 deletion(-)

Qemu files changed

 hw/vfio_pci.c              | 123 +++++++++++++++++++++++++++++++++++++++++++++
 linux-headers/linux/vfio.h |   1 +
 2 files changed, 124 insertions(+)

[PATCH v5 1/3] VFIO: Wrapper for getting reference to vfio_device from device

[Vijay Mohan Pandarathil]

	- Added vfio_device_get_from_dev() as wrapper to get
          reference to vfio_device from struct device.

	- Added vfio_device_data() as a wrapper to get device_data from
          vfio_device.

Signed-off-by: Vijay Mohan Pandarathil <vijaymohan.pandarathil@hp.com>
---
 drivers/vfio/vfio.c  | 47 ++++++++++++++++++++++++++++++++++-------------
 include/linux/vfio.h |  3 +++
 2 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 12c264d..863d1d3 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -407,12 +407,13 @@ static void vfio_device_release(struct kref *kref)
 }
 
 /* Device reference always implies a group reference */
-static void vfio_device_put(struct vfio_device *device)
+void vfio_device_put(struct vfio_device *device)
 {
 	struct vfio_group *group = device->group;
 	kref_put_mutex(&device->kref, vfio_device_release, &group->device_lock);
 	vfio_group_put(group);
 }
+EXPORT_SYMBOL_GPL(vfio_device_put);
 
 static void vfio_device_get(struct vfio_device *device)
 {
@@ -642,8 +643,12 @@ int vfio_add_group_dev(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(vfio_add_group_dev);
 
-/* Test whether a struct device is present in our tracking */
-static bool vfio_dev_present(struct device *dev)
+/**
+ * This does a get on the vfio_device from device.
+ * Callers of this function will have to call vfio_put_device() to
+ * remove the reference.
+ */
+struct vfio_device *vfio_device_get_from_dev(struct device *dev)
 {
 	struct iommu_group *iommu_group;
 	struct vfio_group *group;
@@ -651,25 +656,41 @@ static bool vfio_dev_present(struct device *dev)
 
 	iommu_group = iommu_group_get(dev);
 	if (!iommu_group)
-		return false;
+		return NULL;
 
 	group = vfio_group_get_from_iommu(iommu_group);
 	if (!group) {
 		iommu_group_put(iommu_group);
-		return false;
+		return NULL;
 	}
 
 	device = vfio_group_get_device(group, dev);
-	if (!device) {
-		vfio_group_put(group);
-		iommu_group_put(iommu_group);
-		return false;
-	}
-
-	vfio_device_put(device);
 	vfio_group_put(group);
 	iommu_group_put(iommu_group);
-	return true;
+	return device;
+}
+EXPORT_SYMBOL_GPL(vfio_device_get_from_dev);
+
+/*
+ * Caller must hold a reference to the vfio_device
+ */
+void *vfio_device_data(struct vfio_device *device)
+{
+	return device->device_data;
+}
+EXPORT_SYMBOL_GPL(vfio_device_data);
+
+/* Test whether a struct device is present in our tracking */
+static bool vfio_dev_present(struct device *dev)
+{
+	struct vfio_device *device;
+
+	device = vfio_device_get_from_dev(dev);
+	if (device) {
+		vfio_device_put(device);
+		return true;
+	} else
+		return false;
 }
 
 /*
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index ab9e862..ac8d488 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -45,6 +45,9 @@ extern int vfio_add_group_dev(struct device *dev,
 			      void *device_data);
 
 extern void *vfio_del_group_dev(struct device *dev);
+extern struct vfio_device *vfio_device_get_from_dev(struct device *dev);
+extern void vfio_device_put(struct vfio_device *device);
+extern void *vfio_device_data(struct vfio_device *device);
 
 /**
  * struct vfio_iommu_driver_ops - VFIO IOMMU driver callbacks
-- 
1.7.11.3

[PATCH v5 2/3] VFIO-AER: Vfio-pci driver changes for supporting AER

[Vijay Mohan Pandarathil]

	- New VFIO_SET_IRQ ioctl option to pass the eventfd that is signaled when
          an error occurs in the vfio_pci_device

	- Register pci_error_handler for the vfio_pci driver

	- When the device encounters an error, the error handler registered by
          the vfio_pci driver gets invoked by the AER infrastructure

	- In the error handler, signal the eventfd registered for the device.

	- This results in the qemu eventfd handler getting invoked and
          appropriate action taken for the guest.

Signed-off-by: Vijay Mohan Pandarathil <vijaymohan.pandarathil@hp.com>
---
 drivers/vfio/pci/vfio_pci.c         | 44 ++++++++++++++++++++++++++++++++-
 drivers/vfio/pci/vfio_pci_intrs.c   | 49 +++++++++++++++++++++++++++++++++++++
 drivers/vfio/pci/vfio_pci_private.h |  1 +
 include/uapi/linux/vfio.h           |  1 +
 4 files changed, 94 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index b28e66c..cd99321 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -196,7 +196,9 @@ static int vfio_pci_get_irq_count(struct vfio_pci_device *vdev, int irq_type)
 
 			return (flags & PCI_MSIX_FLAGS_QSIZE) + 1;
 		}
-	}
+	} else if (irq_type == VFIO_PCI_ERR_IRQ_INDEX)
+		if (pci_is_pcie(vdev->pdev))
+			return 1;
 
 	return 0;
 }
@@ -302,6 +304,17 @@ static long vfio_pci_ioctl(void *device_data,
 		if (info.argsz < minsz || info.index >= VFIO_PCI_NUM_IRQS)
 			return -EINVAL;
 
+		switch (info.index) {
+		case VFIO_PCI_INTX_IRQ_INDEX ... VFIO_PCI_MSIX_IRQ_INDEX:
+			break;
+		case VFIO_PCI_ERR_IRQ_INDEX:
+			if (pci_is_pcie(vdev->pdev))
+				break;
+		/* pass thru to return error */
+		default:
+			return -EINVAL;
+		}
+
 		info.flags = VFIO_IRQ_INFO_EVENTFD;
 
 		info.count = vfio_pci_get_irq_count(vdev, info.index);
@@ -538,11 +551,40 @@ static void vfio_pci_remove(struct pci_dev *pdev)
 	kfree(vdev);
 }
 
+static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
+						  pci_channel_state_t state)
+{
+	struct vfio_pci_device *vdev;
+	struct vfio_device *device;
+
+	device = vfio_device_get_from_dev(&pdev->dev);
+	if (device == NULL)
+		return PCI_ERS_RESULT_DISCONNECT;
+
+	vdev = vfio_device_data(device);
+	if (vdev == NULL) {
+		vfio_device_put(device);
+		return PCI_ERS_RESULT_DISCONNECT;
+	}
+
+	if (vdev->err_trigger)
+		eventfd_signal(vdev->err_trigger, 1);
+
+	vfio_device_put(device);
+
+	return PCI_ERS_RESULT_CAN_RECOVER;
+}
+
+static struct pci_error_handlers vfio_err_handlers = {
+	.error_detected = vfio_pci_aer_err_detected,
+};
+
 static struct pci_driver vfio_pci_driver = {
 	.name		= "vfio-pci",
 	.id_table	= NULL, /* only dynamic ids */
 	.probe		= vfio_pci_probe,
 	.remove		= vfio_pci_remove,
+	.err_handler	= &vfio_err_handlers,
 };
 
 static void __exit vfio_pci_cleanup(void)
diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index 3639371..4a29830 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -745,6 +745,48 @@ static int vfio_pci_set_msi_trigger(struct vfio_pci_device *vdev,
 	return 0;
 }
 
+static int vfio_pci_set_err_trigger(struct vfio_pci_device *vdev,
+				    unsigned index, unsigned start,
+				    unsigned count, uint32_t flags, void *data)
+{
+	int32_t fd = *(int32_t *)data;
+
+	if ((index != VFIO_PCI_ERR_IRQ_INDEX) ||
+	    !(flags & VFIO_IRQ_SET_DATA_TYPE_MASK))
+		return -EINVAL;
+
+	/* DATA_NONE/DATA_BOOL enables loopback testing */
+
+	if (flags & VFIO_IRQ_SET_DATA_NONE) {
+		if (vdev->err_trigger)
+			eventfd_signal(vdev->err_trigger, 1);
+		return 0;
+	} else if (flags & VFIO_IRQ_SET_DATA_BOOL) {
+		uint8_t trigger = *(uint8_t *)data;
+		if (trigger && vdev->err_trigger)
+			eventfd_signal(vdev->err_trigger, 1);
+		return 0;
+	}
+
+	/* Handle SET_DATA_EVENTFD */
+
+	if (fd == -1) {
+		if (vdev->err_trigger)
+			eventfd_ctx_put(vdev->err_trigger);
+		vdev->err_trigger = NULL;
+		return 0;
+	} else if (fd >= 0) {
+		struct eventfd_ctx *efdctx;
+		efdctx = eventfd_ctx_fdget(fd);
+		if (IS_ERR(efdctx))
+			return PTR_ERR(efdctx);
+		if (vdev->err_trigger)
+			eventfd_ctx_put(vdev->err_trigger);
+		vdev->err_trigger = efdctx;
+		return 0;
+	} else
+		return -EINVAL;
+}
 int vfio_pci_set_irqs_ioctl(struct vfio_pci_device *vdev, uint32_t flags,
 			    unsigned index, unsigned start, unsigned count,
 			    void *data)
@@ -779,6 +821,13 @@ int vfio_pci_set_irqs_ioctl(struct vfio_pci_device *vdev, uint32_t flags,
 			break;
 		}
 		break;
+	case VFIO_PCI_ERR_IRQ_INDEX:
+		switch (flags & VFIO_IRQ_SET_ACTION_TYPE_MASK) {
+		case VFIO_IRQ_SET_ACTION_TRIGGER:
+			if (pci_is_pcie(vdev->pdev))
+				func = vfio_pci_set_err_trigger;
+			break;
+		}
 	}
 
 	if (!func)
diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
index 611827c..daee62f 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -55,6 +55,7 @@ struct vfio_pci_device {
 	bool			bardirty;
 	struct pci_saved_state	*pci_saved_state;
 	atomic_t		refcnt;
+	struct eventfd_ctx	*err_trigger;
 };
 
 #define is_intx(vdev) (vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX)
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 4758d1b..7d50af4 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -310,6 +310,7 @@ enum {
 	VFIO_PCI_INTX_IRQ_INDEX,
 	VFIO_PCI_MSI_IRQ_INDEX,
 	VFIO_PCI_MSIX_IRQ_INDEX,
+	VFIO_PCI_ERR_IRQ_INDEX,
 	VFIO_PCI_NUM_IRQS
 };
 
-- 
1.7.11.3

[PATCH v5 3/3] QEMU-AER: Qemu changes to support AER for VFIO-PCI devices

[Vijay Mohan Pandarathil]

	- Create eventfd per vfio device assigned to a guest and register an
          event handler

	- This fd is passed to the vfio_pci driver through the SET_IRQ ioctl

	- When the device encounters an error, the eventfd is signalled
          and the qemu eventfd handler gets invoked.

	- In the handler decide what action to take. Current action taken
          is to stop the guest.

Signed-off-by: Vijay Mohan Pandarathil <vijaymohan.pandarathil@hp.com>
---
 hw/vfio_pci.c              | 123 +++++++++++++++++++++++++++++++++++++++++++++
 linux-headers/linux/vfio.h |   1 +
 2 files changed, 124 insertions(+)

diff --git a/hw/vfio_pci.c b/hw/vfio_pci.c
index ad9ae36..3c78771 100644
--- a/hw/vfio_pci.c
+++ b/hw/vfio_pci.c
@@ -38,6 +38,7 @@
 #include "qemu/error-report.h"
 #include "qemu/queue.h"
 #include "qemu/range.h"
+#include "sysemu/sysemu.h"
 
 /* #define DEBUG_VFIO */
 #ifdef DEBUG_VFIO
@@ -129,7 +130,9 @@ typedef struct VFIODevice {
     PCIHostDeviceAddress host;
     QLIST_ENTRY(VFIODevice) next;
     struct VFIOGroup *group;
+    EventNotifier err_notifier;
     bool reset_works;
+    bool pci_aer;
 } VFIODevice;
 
 typedef struct VFIOGroup {
@@ -1802,6 +1805,7 @@ static int vfio_get_device(VFIOGroup *group, const char *name, VFIODevice *vdev)
 {
     struct vfio_device_info dev_info = { .argsz = sizeof(dev_info) };
     struct vfio_region_info reg_info = { .argsz = sizeof(reg_info) };
+    struct vfio_irq_info irq_info = { .argsz = sizeof(irq_info) };
     int ret, i;
 
     ret = ioctl(group->fd, VFIO_GROUP_GET_DEVICE_FD, name);
@@ -1904,6 +1908,18 @@ static int vfio_get_device(VFIOGroup *group, const char *name, VFIODevice *vdev)
     }
     vdev->config_offset = reg_info.offset;
 
+    irq_info.index = VFIO_PCI_ERR_IRQ_INDEX;
+
+    ret = ioctl(vdev->fd, VFIO_DEVICE_GET_IRQ_INFO, &irq_info);
+    if (ret) {
+        /* This can fail for an old kernel or legacy PCI dev */
+        DPRINTF("VFIO_DEVICE_GET_IRQ_INFO failure ret=%d\n", ret);
+        ret = 0;
+    } else if (irq_info.count == 1) {
+        vdev->pci_aer = true;
+    } else {
+        error_report("vfio: Warning: Could not enable error recovery for the device\n");
+    }
 error:
     if (ret) {
         QLIST_REMOVE(vdev, next);
@@ -1925,6 +1941,110 @@ static void vfio_put_device(VFIODevice *vdev)
     }
 }
 
+static void vfio_err_notifier_handler(void *opaque)
+{
+    VFIODevice *vdev = opaque;
+
+    if (!event_notifier_test_and_clear(&vdev->err_notifier)) {
+        return;
+    }
+
+    /*
+     * TBD. Retrieve the error details and decide what action
+     * needs to be taken. One of the actions could be to pass
+     * the error to the guest and have the guest driver recover
+     * from the error. This requires that PCIe capabilities be
+     * exposed to the guest. For now, we just terminate the
+     * guest to contain the error.
+     */
+
+    error_report("%s (%04x:%02x:%02x.%x)"
+        "Unrecoverable error detected...\n"
+        "Please collect any data possible and then kill the guest",
+        __func__, vdev->host.domain, vdev->host.bus,
+        vdev->host.slot, vdev->host.function);
+
+    vm_stop(RUN_STATE_IO_ERROR);
+}
+
+/*
+ * Registers error notifier for devices supporting error recovery.
+ * If we encounter a failure in this function, we report an error
+ * and continue after disabling error recovery support for the
+ * device.
+ */
+static void vfio_register_err_notifier(VFIODevice *vdev)
+{
+    int ret;
+    int argsz;
+    struct vfio_irq_set *irq_set;
+    int32_t *pfd;
+
+    if (!vdev->pci_aer) {
+        return;
+    }
+
+    if (event_notifier_init(&vdev->err_notifier, 0)) {
+        error_report("vfio: Warning: Unable to init event notifier for error detection\n");
+        vdev->pci_aer = false;
+        return;
+    }
+
+    argsz = sizeof(*irq_set) + sizeof(*pfd);
+
+    irq_set = g_malloc0(argsz);
+    irq_set->argsz = argsz;
+    irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD |
+                     VFIO_IRQ_SET_ACTION_TRIGGER;
+    irq_set->index = VFIO_PCI_ERR_IRQ_INDEX;
+    irq_set->start = 0;
+    irq_set->count = 1;
+    pfd = (int32_t *)&irq_set->data;
+
+    *pfd = event_notifier_get_fd(&vdev->err_notifier);
+    qemu_set_fd_handler(*pfd, vfio_err_notifier_handler, NULL, vdev);
+
+    ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
+    if (ret) {
+        error_report("vfio: Failed to set up error notification\n");
+        qemu_set_fd_handler(*pfd, NULL, NULL, vdev);
+        event_notifier_cleanup(&vdev->err_notifier);
+        vdev->pci_aer = false;
+    }
+    g_free(irq_set);
+}
+static void vfio_unregister_err_notifier(VFIODevice *vdev)
+{
+    int argsz;
+    struct vfio_irq_set *irq_set;
+    int32_t *pfd;
+    int ret;
+
+    if (!vdev->pci_aer) {
+        return;
+    }
+
+    argsz = sizeof(*irq_set) + sizeof(*pfd);
+
+    irq_set = g_malloc0(argsz);
+    irq_set->argsz = argsz;
+    irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD |
+                     VFIO_IRQ_SET_ACTION_TRIGGER;
+    irq_set->index = VFIO_PCI_ERR_IRQ_INDEX;
+    irq_set->start = 0;
+    irq_set->count = 1;
+    pfd = (int32_t *)&irq_set->data;
+    *pfd = -1;
+
+    ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
+    if (ret) {
+        error_report("vfio: Failed to de-assign error fd: %d\n", ret);
+    }
+    g_free(irq_set);
+    qemu_set_fd_handler(event_notifier_get_fd(&vdev->err_notifier),
+                        NULL, NULL, vdev);
+    event_notifier_cleanup(&vdev->err_notifier);
+}
 static int vfio_initfn(PCIDevice *pdev)
 {
     VFIODevice *pvdev, *vdev = DO_UPCAST(VFIODevice, pdev, pdev);
@@ -2035,6 +2155,8 @@ static int vfio_initfn(PCIDevice *pdev)
         }
     }
 
+    vfio_register_err_notifier(vdev);
+
     return 0;
 
 out_teardown:
@@ -2052,6 +2174,7 @@ static void vfio_exitfn(PCIDevice *pdev)
     VFIODevice *vdev = DO_UPCAST(VFIODevice, pdev, pdev);
     VFIOGroup *group = vdev->group;
 
+    vfio_unregister_err_notifier(vdev);
     pci_device_set_intx_routing_notifier(&vdev->pdev, NULL);
     vfio_disable_interrupts(vdev);
     if (vdev->intx.mmap_timer) {
diff --git a/linux-headers/linux/vfio.h b/linux-headers/linux/vfio.h
index f787b72..6b20849 100644
--- a/linux-headers/linux/vfio.h
+++ b/linux-headers/linux/vfio.h
@@ -310,6 +310,7 @@ enum {
 	VFIO_PCI_INTX_IRQ_INDEX,
 	VFIO_PCI_MSI_IRQ_INDEX,
 	VFIO_PCI_MSIX_IRQ_INDEX,
+	VFIO_PCI_ERR_IRQ_INDEX,
 	VFIO_PCI_NUM_IRQS
 };
 
-- 
1.7.11.3

Re: [PATCH v5 1/3] VFIO: Wrapper for getting reference to vfio_device from device

[Alex Williamson]

On Sat, 2013-02-23 at 23:25 -0600, Vijay Mohan Pandarathil wrote:
> 	- Added vfio_device_get_from_dev() as wrapper to get
>           reference to vfio_device from struct device.
> 
> 	- Added vfio_device_data() as a wrapper to get device_data from
>           vfio_device.
> 
> Signed-off-by: Vijay Mohan Pandarathil <vijaymohan.pandarathil@hp.com>
> ---
>  drivers/vfio/vfio.c  | 47 ++++++++++++++++++++++++++++++++++-------------
>  include/linux/vfio.h |  3 +++
>  2 files changed, 37 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index 12c264d..863d1d3 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -407,12 +407,13 @@ static void vfio_device_release(struct kref *kref)
>  }
>  
>  /* Device reference always implies a group reference */
> -static void vfio_device_put(struct vfio_device *device)
> +void vfio_device_put(struct vfio_device *device)
>  {
>  	struct vfio_group *group = device->group;
>  	kref_put_mutex(&device->kref, vfio_device_release, &group->device_lock);
>  	vfio_group_put(group);
>  }
> +EXPORT_SYMBOL_GPL(vfio_device_put);
>  
>  static void vfio_device_get(struct vfio_device *device)
>  {
> @@ -642,8 +643,12 @@ int vfio_add_group_dev(struct device *dev,
>  }
>  EXPORT_SYMBOL_GPL(vfio_add_group_dev);
>  
> -/* Test whether a struct device is present in our tracking */
> -static bool vfio_dev_present(struct device *dev)
> +/**
> + * This does a get on the vfio_device from device.
> + * Callers of this function will have to call vfio_put_device() to
> + * remove the reference.
> + */
> +struct vfio_device *vfio_device_get_from_dev(struct device *dev)
>  {

I cc'd you on a patch that changes vfio_dev_present to fix a bug where
the device to iommu group lookup has been shutdown.  Using it for this
purpose probably has the same bug.  That code is in my next branch and
in the most reset pull request to Linus.

I think instead the code becomes much more simple.  We're registering a
callback for a struct device for which vfio-pci is the driver.  During
driver release we disable that callback for the device.  Thus during the
callback, we know the device is owned by vfio-pci, which means that the
drvdata has what we need.  So I think vfio_device_get_from_dev() simply
becomes:

struct vfio_device *vfio_get_device_from_dev(struct device *dev)
{
       struct vfio_device *device = dev_get_drvdata(dev);

       vfio_device_get(device);

       return device;
}
EXPORT_SYMBOL_GPL(vfio_get_device_from_dev);

Thanks,
Alex

>  	struct iommu_group *iommu_group;
>  	struct vfio_group *group;
> @@ -651,25 +656,41 @@ static bool vfio_dev_present(struct device *dev)
>  
>  	iommu_group = iommu_group_get(dev);
>  	if (!iommu_group)
> -		return false;
> +		return NULL;
>  
>  	group = vfio_group_get_from_iommu(iommu_group);
>  	if (!group) {
>  		iommu_group_put(iommu_group);
> -		return false;
> +		return NULL;
>  	}
>  
>  	device = vfio_group_get_device(group, dev);
> -	if (!device) {
> -		vfio_group_put(group);
> -		iommu_group_put(iommu_group);
> -		return false;
> -	}
> -
> -	vfio_device_put(device);
>  	vfio_group_put(group);
>  	iommu_group_put(iommu_group);
> -	return true;
> +	return device;
> +}
> +EXPORT_SYMBOL_GPL(vfio_device_get_from_dev);
> +
> +/*
> + * Caller must hold a reference to the vfio_device
> + */
> +void *vfio_device_data(struct vfio_device *device)
> +{
> +	return device->device_data;
> +}
> +EXPORT_SYMBOL_GPL(vfio_device_data);
> +
> +/* Test whether a struct device is present in our tracking */
> +static bool vfio_dev_present(struct device *dev)
> +{
> +	struct vfio_device *device;
> +
> +	device = vfio_device_get_from_dev(dev);
> +	if (device) {
> +		vfio_device_put(device);
> +		return true;
> +	} else
> +		return false;
>  }
>  
>  /*
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index ab9e862..ac8d488 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -45,6 +45,9 @@ extern int vfio_add_group_dev(struct device *dev,
>  			      void *device_data);
>  
>  extern void *vfio_del_group_dev(struct device *dev);
> +extern struct vfio_device *vfio_device_get_from_dev(struct device *dev);
> +extern void vfio_device_put(struct vfio_device *device);
> +extern void *vfio_device_data(struct vfio_device *device);
>  
>  /**
>   * struct vfio_iommu_driver_ops - VFIO IOMMU driver callbacks