[RFC PATCH 1/5] PCI: Refuse function reset of an SR-IOV PF with enabled VFs

[Alex Williamson <alex.williamson@nvidia.com>]

pci_reset_function() and its locked and try variants are intended to
provide a function-scoped reset.  The bus and slot methods supporting
this interface refuse when sibling or subordinate devices are present.
SR-IOV VFs however, are not currently considered in this scope.

Correct this oversight by testing for non-zero VF count in calls
through the pci_reset_function() interfaces.  This test needs to occur
under device_lock to avoid races with .sriov_configure.  It should
also occur before pci_dev_save_and_disable() to avoid calling
potentially destructive reset hooks.  Tests are therefore added
to each of pci_reset_function(), pci_reset_function_locked(), and
pci_try_reset_function().

The __pci_reset_function_locked() interface remains a low-level
primitive depending on the caller to perform such tests as necessary.
The vfio_pci_core use case of __pci_reset_function_locked() is pulled
through with this test.  Other use cases, such as xen-pciback, that
don't obviously support or prevent binding to SR-IOV enabled PFs will
need to decide whether VFs are possible and can be preserved.
Additionally, direct callers of sriov_enable() that do not hold
device_lock (lpfc) are considered a preexisting, non-compliance issue.

Fixes: dd7cc44d0bce ("PCI: add SR-IOV API for Physical Function driver")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
---
 drivers/pci/pci.c                | 19 +++++++++++++++++++
 drivers/vfio/pci/vfio_pci_core.c |  4 +++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 77b17b13ee61..b40b00c0c0c9 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5222,11 +5222,22 @@ int pci_reset_function(struct pci_dev *dev)
 		pci_dev_lock(bridge);
 
 	pci_dev_lock(dev);
+
+	/*
+	 * Reset of an SR-IOV PF necessarily resets any active VFs.  Such resets are
+	 * beyond the scope advertised for pci_reset_function() and variants, refuse.
+	 */
+	if (pci_num_vf(dev) > 0) {
+		rc = -ENOTTY;
+		goto unlock;
+	}
+
 	pci_dev_save_and_disable(dev);
 
 	rc = __pci_reset_function_locked(dev);
 
 	pci_dev_restore(dev);
+unlock:
 	pci_dev_unlock(dev);
 
 	if (bridge)
@@ -5264,6 +5275,9 @@ int pci_reset_function_locked(struct pci_dev *dev)
 	if (!pci_reset_supported(dev))
 		return -ENOTTY;
 
+	if (pci_num_vf(dev) > 0)
+		return -ENOTTY;
+
 	pci_dev_save_and_disable(dev);
 
 	rc = __pci_reset_function_locked(dev);
@@ -5290,6 +5304,11 @@ int pci_try_reset_function(struct pci_dev *dev)
 	if (!pci_dev_trylock(dev))
 		return -EAGAIN;
 
+	if (pci_num_vf(dev) > 0) {
+		pci_dev_unlock(dev);
+		return -ENOTTY;
+	}
+
 	pci_dev_save_and_disable(dev);
 	rc = __pci_reset_function_locked(dev);
 	pci_dev_restore(dev);
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 3f11a9624b9c..9757b171791c 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -790,7 +790,9 @@ void vfio_pci_core_disable(struct vfio_pci_core_device *vdev)
 		if (bridge && !pci_dev_trylock(bridge))
 			goto out_restore_state;
 		if (pci_dev_trylock(pdev)) {
-			if (!__pci_reset_function_locked(pdev))
+			/* Enforce function scope under lock for SR-IOV PFs */
+			if (!pci_num_vf(pdev) &&
+			    !__pci_reset_function_locked(pdev))
 				vdev->needs_reset = false;
 			pci_dev_unlock(pdev);
 		}
-- 
2.53.0