[PATCH] vfio/pci: Remove vfio_device_get_from_dev()

[PATCH] vfio/pci: Remove vfio_device_get_from_dev()

[Jason Gunthorpe]

The last user of this function is in PCI callbacks that want to convert
their struct pci_dev to a vfio_device. Instead of searching use the
vfio_device available trivially through the drvdata.

When a callback in the device_driver is called, the caller must hold the
device_lock() on dev. The purpose of the device_lock is to prevent
remove() from being called (see __device_release_driver), and allow the
driver to safely interact with its drvdata without races.

The PCI core correctly follows this and holds the device_lock() when
calling error_detected (see report_error_detected) and
sriov_configure (see sriov_numvfs_store).

Further, since the drvdata holds a positive refcount on the vfio_device
any access of the drvdata, under the driver_lock, from a driver callback
needs no further protection or refcounting.

Thus the remark in the vfio_device_get_from_dev() comment does not apply
here, VFIO PCI drivers all call vfio_unregister_group_dev() from their
remove callbacks under the driver lock and cannot race with the remaining
callers.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 .../vfio/pci/hisilicon/hisi_acc_vfio_pci.c    | 12 +++++-
 drivers/vfio/pci/mlx5/main.c                  | 10 ++++-
 drivers/vfio/pci/vfio_pci.c                   | 18 +++++++-
 drivers/vfio/pci/vfio_pci_core.c              | 42 ++++---------------
 drivers/vfio/vfio.c                           | 26 +-----------
 include/linux/vfio.h                          |  2 -
 include/linux/vfio_pci_core.h                 |  9 ++--
 7 files changed, 50 insertions(+), 69 deletions(-)

This depends on the gvt rework from Christoph.

diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
index 767b5d47631a49..14bf85ff6cbe96 100644
--- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
+++ b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
@@ -1305,9 +1305,19 @@ static const struct pci_device_id hisi_acc_vfio_pci_table[] = {
 
 MODULE_DEVICE_TABLE(pci, hisi_acc_vfio_pci_table);
 
+static pci_ers_result_t hisi_acc_aer_err_detected(struct pci_dev *pdev,
+						  pci_channel_state_t state)
+{
+	struct hisi_acc_vf_core_device *hisi_acc_vdev =
+		dev_get_drvdata(&pdev->dev);
+
+	return vfio_pci_core_aer_err_detected(&hisi_acc_vdev->core_device,
+					      state);
+}
+
 static const struct pci_error_handlers hisi_acc_vf_err_handlers = {
 	.reset_done = hisi_acc_vf_pci_aer_reset_done,
-	.error_detected = vfio_pci_core_aer_err_detected,
+	.error_detected = hisi_acc_aer_err_detected,
 };
 
 static struct pci_driver hisi_acc_vfio_pci_driver = {
diff --git a/drivers/vfio/pci/mlx5/main.c b/drivers/vfio/pci/mlx5/main.c
index bbec5d288fee97..fbba1d52a4cf64 100644
--- a/drivers/vfio/pci/mlx5/main.c
+++ b/drivers/vfio/pci/mlx5/main.c
@@ -643,9 +643,17 @@ static const struct pci_device_id mlx5vf_pci_table[] = {
 
 MODULE_DEVICE_TABLE(pci, mlx5vf_pci_table);
 
+static pci_ers_result_t mlx5vf_pci_aer_err_detected(struct pci_dev *pdev,
+						    pci_channel_state_t state)
+{
+	struct mlx5vf_pci_core_device *mvdev = dev_get_drvdata(&pdev->dev);
+
+	return vfio_pci_core_aer_err_detected(&mvdev->core_device, state);
+}
+
 static const struct pci_error_handlers mlx5vf_err_handlers = {
 	.reset_done = mlx5vf_pci_aer_reset_done,
-	.error_detected = vfio_pci_core_aer_err_detected,
+	.error_detected = mlx5vf_pci_aer_err_detected,
 };
 
 static struct pci_driver mlx5vf_pci_driver = {
diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 2b047469e02fee..6045aaf64f5a40 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -174,10 +174,12 @@ static void vfio_pci_remove(struct pci_dev *pdev)
 
 static int vfio_pci_sriov_configure(struct pci_dev *pdev, int nr_virtfn)
 {
+	struct vfio_pci_core_device *vdev = dev_get_drvdata(&pdev->dev);
+
 	if (!enable_sriov)
 		return -ENOENT;
 
-	return vfio_pci_core_sriov_configure(pdev, nr_virtfn);
+	return vfio_pci_core_sriov_configure(vdev, nr_virtfn);
 }
 
 static const struct pci_device_id vfio_pci_table[] = {
@@ -187,13 +189,25 @@ static const struct pci_device_id vfio_pci_table[] = {
 
 MODULE_DEVICE_TABLE(pci, vfio_pci_table);
 
+static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
+						  pci_channel_state_t state)
+{
+	struct vfio_pci_core_device *vdev = dev_get_drvdata(&pdev->dev);
+
+	return vfio_pci_core_aer_err_detected(vdev, state);
+}
+
+static const struct pci_error_handlers vfio_pci_err_handlers = {
+	.error_detected = vfio_pci_aer_err_detected,
+};
+
 static struct pci_driver vfio_pci_driver = {
 	.name			= "vfio-pci",
 	.id_table		= vfio_pci_table,
 	.probe			= vfio_pci_probe,
 	.remove			= vfio_pci_remove,
 	.sriov_configure	= vfio_pci_sriov_configure,
-	.err_handler		= &vfio_pci_core_err_handlers,
+	.err_handler		= &vfio_pci_err_handlers,
 };
 
 static void __init vfio_pci_fill_ids(void)
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 06b6f3594a1316..9778d713f546d2 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1890,9 +1890,7 @@ EXPORT_SYMBOL_GPL(vfio_pci_core_register_device);
 
 void vfio_pci_core_unregister_device(struct vfio_pci_core_device *vdev)
 {
-	struct pci_dev *pdev = vdev->pdev;
-
-	vfio_pci_core_sriov_configure(pdev, 0);
+	vfio_pci_core_sriov_configure(vdev, 0);
 
 	vfio_unregister_group_dev(&vdev->vdev);
 
@@ -1904,18 +1902,10 @@ void vfio_pci_core_unregister_device(struct vfio_pci_core_device *vdev)
 }
 EXPORT_SYMBOL_GPL(vfio_pci_core_unregister_device);
 
-pci_ers_result_t vfio_pci_core_aer_err_detected(struct pci_dev *pdev,
-						pci_channel_state_t state)
+pci_ers_result_t
+vfio_pci_core_aer_err_detected(struct vfio_pci_core_device *vdev,
+			       pci_channel_state_t state)
 {
-	struct vfio_pci_core_device *vdev;
-	struct vfio_device *device;
-
-	device = vfio_device_get_from_dev(&pdev->dev);
-	if (device == NULL)
-		return PCI_ERS_RESULT_DISCONNECT;
-
-	vdev = container_of(device, struct vfio_pci_core_device, vdev);
-
 	mutex_lock(&vdev->igate);
 
 	if (vdev->err_trigger)
@@ -1923,26 +1913,18 @@ pci_ers_result_t vfio_pci_core_aer_err_detected(struct pci_dev *pdev,
 
 	mutex_unlock(&vdev->igate);
 
-	vfio_device_put(device);
-
 	return PCI_ERS_RESULT_CAN_RECOVER;
 }
 EXPORT_SYMBOL_GPL(vfio_pci_core_aer_err_detected);
 
-int vfio_pci_core_sriov_configure(struct pci_dev *pdev, int nr_virtfn)
+int vfio_pci_core_sriov_configure(struct vfio_pci_core_device *vdev,
+				  int nr_virtfn)
 {
-	struct vfio_pci_core_device *vdev;
-	struct vfio_device *device;
+	struct pci_dev *pdev = vdev->pdev;
 	int ret = 0;
 
 	device_lock_assert(&pdev->dev);
 
-	device = vfio_device_get_from_dev(&pdev->dev);
-	if (!device)
-		return -ENODEV;
-
-	vdev = container_of(device, struct vfio_pci_core_device, vdev);
-
 	if (nr_virtfn) {
 		mutex_lock(&vfio_pci_sriov_pfs_mutex);
 		/*
@@ -1960,8 +1942,7 @@ int vfio_pci_core_sriov_configure(struct pci_dev *pdev, int nr_virtfn)
 		ret = pci_enable_sriov(pdev, nr_virtfn);
 		if (ret)
 			goto out_del;
-		ret = nr_virtfn;
-		goto out_put;
+		return ret;
 	}
 
 	pci_disable_sriov(pdev);
@@ -1971,17 +1952,10 @@ int vfio_pci_core_sriov_configure(struct pci_dev *pdev, int nr_virtfn)
 	list_del_init(&vdev->sriov_pfs_item);
 out_unlock:
 	mutex_unlock(&vfio_pci_sriov_pfs_mutex);
-out_put:
-	vfio_device_put(device);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(vfio_pci_core_sriov_configure);
 
-const struct pci_error_handlers vfio_pci_core_err_handlers = {
-	.error_detected = vfio_pci_core_aer_err_detected,
-};
-EXPORT_SYMBOL_GPL(vfio_pci_core_err_handlers);
-
 static bool vfio_dev_in_groups(struct vfio_pci_core_device *vdev,
 			       struct vfio_pci_group_info *groups)
 {
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index a4555014bd1e72..74e4197105904e 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -492,12 +492,11 @@ static struct vfio_group *vfio_group_get_from_dev(struct device *dev)
  * Device objects - create, release, get, put, search
  */
 /* Device reference always implies a group reference */
-void vfio_device_put(struct vfio_device *device)
+static void vfio_device_put(struct vfio_device *device)
 {
 	if (refcount_dec_and_test(&device->refcount))
 		complete(&device->comp);
 }
-EXPORT_SYMBOL_GPL(vfio_device_put);
 
 static bool vfio_device_try_get(struct vfio_device *device)
 {
@@ -831,29 +830,6 @@ int vfio_register_emulated_iommu_dev(struct vfio_device *device)
 }
 EXPORT_SYMBOL_GPL(vfio_register_emulated_iommu_dev);
 
-/*
- * Get a reference to the vfio_device for a device.  Even if the
- * caller thinks they own the device, they could be racing with a
- * release call path, so we can't trust drvdata for the shortcut.
- * Go the long way around, from the iommu_group to the vfio_group
- * to the vfio_device.
- */
-struct vfio_device *vfio_device_get_from_dev(struct device *dev)
-{
-	struct vfio_group *group;
-	struct vfio_device *device;
-
-	group = vfio_group_get_from_dev(dev);
-	if (!group)
-		return NULL;
-
-	device = vfio_group_get_device(group, dev);
-	vfio_group_put(group);
-
-	return device;
-}
-EXPORT_SYMBOL_GPL(vfio_device_get_from_dev);
-
 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 66dda06ec42d1b..ae06731d947bf7 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -125,8 +125,6 @@ void vfio_uninit_group_dev(struct vfio_device *device);
 int vfio_register_group_dev(struct vfio_device *device);
 int vfio_register_emulated_iommu_dev(struct vfio_device *device);
 void vfio_unregister_group_dev(struct vfio_device *device);
-extern struct vfio_device *vfio_device_get_from_dev(struct device *dev);
-extern void vfio_device_put(struct vfio_device *device);
 
 int vfio_assign_device_set(struct vfio_device *device, void *set_id);
 
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 48f2dd3c568c83..a0978ce126395c 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -227,8 +227,8 @@ void vfio_pci_core_init_device(struct vfio_pci_core_device *vdev,
 int vfio_pci_core_register_device(struct vfio_pci_core_device *vdev);
 void vfio_pci_core_uninit_device(struct vfio_pci_core_device *vdev);
 void vfio_pci_core_unregister_device(struct vfio_pci_core_device *vdev);
-int vfio_pci_core_sriov_configure(struct pci_dev *pdev, int nr_virtfn);
-extern const struct pci_error_handlers vfio_pci_core_err_handlers;
+int vfio_pci_core_sriov_configure(struct vfio_pci_core_device *vdev,
+				  int nr_virtfn);
 long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
 		unsigned long arg);
 int vfio_pci_core_ioctl_feature(struct vfio_device *device, u32 flags,
@@ -243,8 +243,9 @@ int vfio_pci_core_match(struct vfio_device *core_vdev, char *buf);
 int vfio_pci_core_enable(struct vfio_pci_core_device *vdev);
 void vfio_pci_core_disable(struct vfio_pci_core_device *vdev);
 void vfio_pci_core_finish_enable(struct vfio_pci_core_device *vdev);
-pci_ers_result_t vfio_pci_core_aer_err_detected(struct pci_dev *pdev,
-						pci_channel_state_t state);
+pci_ers_result_t
+vfio_pci_core_aer_err_detected(struct vfio_pci_core_device *vdev,
+			       pci_channel_state_t state);
 
 static inline bool vfio_pci_is_vga(struct pci_dev *pdev)
 {

base-commit: 1d0b96c15ee71167d8020446b608a0ed6a70d4b3
-- 
2.36.0

RE: [PATCH] vfio/pci: Remove vfio_device_get_from_dev()

[Tian, Kevin]

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Tuesday, April 26, 2022 7:01 AM
> 
> The last user of this function is in PCI callbacks that want to convert
> their struct pci_dev to a vfio_device. Instead of searching use the
> vfio_device available trivially through the drvdata.
> 
> When a callback in the device_driver is called, the caller must hold the
> device_lock() on dev. The purpose of the device_lock is to prevent
> remove() from being called (see __device_release_driver), and allow the
> driver to safely interact with its drvdata without races.
> 
> The PCI core correctly follows this and holds the device_lock() when
> calling error_detected (see report_error_detected) and
> sriov_configure (see sriov_numvfs_store).

Above is clear for the change in this patch.

> 
> Further, since the drvdata holds a positive refcount on the vfio_device
> any access of the drvdata, under the driver_lock, from a driver callback
> needs no further protection or refcounting.

but I'm confused by driver_lock here and below. Which driver_lock is
referred to in this context?

> 
> Thus the remark in the vfio_device_get_from_dev() comment does not apply
> here, VFIO PCI drivers all call vfio_unregister_group_dev() from their
> remove callbacks under the driver lock and cannot race with the remaining
> callers.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Nevertheless, this patch sounds the correct thing to do:

Reviewed-by: Kevin Tian <kevin.tian@intel.com>

but with one nit...

[...]
> @@ -1960,8 +1942,7 @@ int vfio_pci_core_sriov_configure(struct pci_dev
> *pdev, int nr_virtfn)
>  		ret = pci_enable_sriov(pdev, nr_virtfn);
>  		if (ret)
>  			goto out_del;
> -		ret = nr_virtfn;
> -		goto out_put;
> +		return ret;

pci_enable_sriov() returns 0 on success while .sriov_configure()
is expected to return enabled nr_virtfn on success. Above changes
the semantics.

Re: [PATCH] vfio/pci: Remove vfio_device_get_from_dev()

[Jason Gunthorpe]

On Tue, Apr 26, 2022 at 03:51:13AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Tuesday, April 26, 2022 7:01 AM
> > 
> > The last user of this function is in PCI callbacks that want to convert
> > their struct pci_dev to a vfio_device. Instead of searching use the
> > vfio_device available trivially through the drvdata.
> > 
> > When a callback in the device_driver is called, the caller must hold the
> > device_lock() on dev. The purpose of the device_lock is to prevent
> > remove() from being called (see __device_release_driver), and allow the
> > driver to safely interact with its drvdata without races.
> > 
> > The PCI core correctly follows this and holds the device_lock() when
> > calling error_detected (see report_error_detected) and
> > sriov_configure (see sriov_numvfs_store).
> 
> Above is clear for the change in this patch.
> 
> > 
> > Further, since the drvdata holds a positive refcount on the vfio_device
> > any access of the drvdata, under the driver_lock, from a driver callback
> > needs no further protection or refcounting.
> 
> but I'm confused by driver_lock here and below. Which driver_lock is
> referred to in this context?

That is a typo, it should be device_lock

> > Thus the remark in the vfio_device_get_from_dev() comment does not apply
> > here, VFIO PCI drivers all call vfio_unregister_group_dev() from their
> > remove callbacks under the driver lock and cannot race with the remaining
> > callers.
> > 
> > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> 
> Nevertheless, this patch sounds the correct thing to do:
> 
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> 
> but with one nit...
> 
> [...]
> > @@ -1960,8 +1942,7 @@ int vfio_pci_core_sriov_configure(struct pci_dev
> > *pdev, int nr_virtfn)
> >  		ret = pci_enable_sriov(pdev, nr_virtfn);
> >  		if (ret)
> >  			goto out_del;
> > -		ret = nr_virtfn;
> > -		goto out_put;
> > +		return ret;
> 
> pci_enable_sriov() returns 0 on success while .sriov_configure()
> is expected to return enabled nr_virtfn on success. Above changes
> the semantics.

Arg, I botched it when rebasing over the final version of the rc
patch.. Thanks!

Jason