Re: [RFC PATCH v2 13/16] vfio/pci: Complete recovery in resume()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] PCI: deadlock in AER resume due to recursive pci_bus_sem read lock
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commit ac6b588d8a9a2d9a21c17325b45933f079efe247
Author: Shameer Kolothum <skolothumtho@nvidia.com>

vfio/pci: Complete recovery in resume()

This commit adds the resume() callback to complete host transactions and notify
userspace during VFIO PCI recovery. It restores device state, handles PCI
power state transitions, and finishes restoring hardware state before allowing
accesses.

> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index a7b7499e071c1..d6cc34240b250 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c

[ ... ]

> @@ -2615,6 +2616,87 @@ static pci_ers_result_t vfio_pci_core_aer_slot_reset(struct pci_dev *pdev)
>  	return PCI_ERS_RESULT_NONE;
>  }
>  
> +static void vfio_pci_core_aer_resume(struct pci_dev *pdev)
> +{
> +	struct vfio_pci_core_device *vdev = dev_get_drvdata(&pdev->dev);

[ ... ]

> +	/*
> +	 * Apply deferred D0 requests before restoring PCI_COMMAND.
> +	 * slot_reset() has already established D0 after a reset.
> +	 */
> +	power_up = vdev->power_up_pending;
> +	vdev->power_up_pending = false;
> +	if (power_up && !(vdev->pci_recovery_flags & VFIO_PCI_RECOVERY_RESET)) {
> +		ret = vfio_pci_set_power_state(vdev, PCI_D0);

[Severity: High]
Can this lead to a deadlock of the PCI subsystem?

An AER recovery event triggers the AER core, which acquires pci_bus_sem for
read via pci_walk_bridge().

The AER resume callback vfio_pci_core_aer_resume() then calls
vfio_pci_set_power_state(), which internally attempts to recursively acquire
pci_bus_sem for read via pcie_aspm_pm_state_change().

If a writer, such as a PCI hotplug event, requests pci_bus_sem between these
two read lock attempts, the second read attempt will deadlock.

While this is noted as an unresolved issue in the series cover letter, is
there a plan to mitigate this recursive lock before merging?

> +		if (ret)
> +			goto out_memory;
> +	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260929173305.204856-1-skolothumtho@nvidia.com?part=13