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

On Tue, Aug 11, 2026 at 10:53:19PM -0600, Alex Williamson wrote:
>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: [email protected]
>Assisted-by: Claude:claude-opus-4-8
>Signed-off-by: Alex Williamson <[email protected]>
>---
> drivers/pci/pci.c                | 19 +++++++++++++++++++
> drivers/vfio/pci/vfio_pci_core.c |  4 +++-
> 2 files changed, 22 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c

[snip]

>index 3f11a9624b9c..9757b171791c 100644
>--- a/drivers/vfio/pci/vfio_pci_core.c
>+++ b/drivers/vfio/pci/vfio_pci_core.c

nit: This probably needs to be a different patch.
>@@ -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);
> 		}

I was worried that this would fall into pci_restore_state() and disable
sriov, but it doesn't since there is a check in pci_restore_iov_state()
that skips disabling sriov if VFs are enabled.

Do you think we should skip the pci_restore_state() in general?
>-- 
>2.53.0
>