Re: [PATCH v4 02/10] PCI: Add additional checks for flr reset

[Benjamin Block]

On Wed, Sep 24, 2025 at 10:16:20AM -0700, Farhan Ali wrote:
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index a3d93d1baee7..327fefc6a1eb 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4576,12 +4576,19 @@ EXPORT_SYMBOL_GPL(pcie_flr);
>   */
>  int pcie_reset_flr(struct pci_dev *dev, bool probe)
>  {
> +	u32 reg;
> +
>  	if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET)
>  		return -ENOTTY;
>  
>  	if (!(dev->devcap & PCI_EXP_DEVCAP_FLR))
>  		return -ENOTTY;
>  
> +	if (pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &reg)) {
> +		pci_warn(dev, "Device unable to do an FLR\n");
> +		return -ENOTTY;
> +	}

Just thinking out loud, not sure whether it make sense, but since you already
read an up-to-date value from the config space, would it make sense to
pull the check above `dev->devcap & PCI_EXP_DEVCAP_FLR` below this read, and
check on the just read `reg`?

Also wondering whether it makes sense to stable-tag this? We've recently seen
"unpleasant" recovery attempts that look like this in the kernel logs:

    [  663.330053] vfio-pci 0007:00:00.1: timed out waiting for pending transaction; performing function level reset anyway
    [  664.730051] vfio-pci 0007:00:00.1: not ready 1023ms after FLR; waiting
    [  665.830023] vfio-pci 0007:00:00.1: not ready 2047ms after FLR; waiting
    [  667.910023] vfio-pci 0007:00:00.1: not ready 4095ms after FLR; waiting
    [  672.070022] vfio-pci 0007:00:00.1: not ready 8191ms after FLR; waiting
    [  680.550025] vfio-pci 0007:00:00.1: not ready 16383ms after FLR; waiting
    [  697.190023] vfio-pci 0007:00:00.1: not ready 32767ms after FLR; waiting
    [  730.470021] vfio-pci 0007:00:00.1: not ready 65535ms after FLR; giving up

The VF here was already dead in the water at that point, so I suspect
`pci_read_config_dword()` might have failed, and so this check would have
failed, and we wouldn't have "wasted" the minute waiting for a FLR that was
never going to happen anyway.


-- 
Best Regards, Benjamin Block        /        Linux on IBM Z Kernel Development
IBM Deutschland Research & Development GmbH    /   https://www.ibm.com/privacy
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