Re: [PATCH 2/3] PCI/IOV: Restore initial VF ReBAR sizes on SR-IOV disable/failure

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Early error returns in sriov_enable() bypass the newly introduced sriov_restore_vf_rebar_initial_sizes() cleanup.
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commit 4da183a318507a36de3ca157ee8755ad1eec90ca
Author: Marcin Bernatowicz <marcin.bernatowicz@linux.intel.com>

PCI/IOV: Restore initial VF ReBAR sizes on SR-IOV disable/failure

This commit introduces a mechanism to restore the initial VF BAR sizes when
SR-IOV is disabled or when enabling it fails. This prevents the PCI core
from persisting inflated VF BAR sizes, which can lead to MMIO space exhaustion.

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5937

> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 217e133a38c73..a05c1be388d2f 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c

[ ... ]

> @@ -687,36 +721,42 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
>  	}
>  	if (nres != iov->nres) {
>  		pci_err(dev, "not enough MMIO resources for SR-IOV\n");
> -		return -ENOMEM;
> +		rc = -ENOMEM;
> +		goto err_restore;
>  	}

Should the earlier error returns in sriov_enable() also jump to err_restore?

There are early validation checks before this point that return directly:

drivers/pci/iov.c:sriov_enable() {
    ...
	pci_read_config_word(dev, iov->pos + PCI_SRIOV_INITIAL_VF, &initial);
	if (initial > iov->total_VFs ||
	    (!(iov->cap & PCI_SRIOV_CAP_VFM) && (initial != iov->total_VFs)))
		return -EIO;

	if (nr_virtfn < 0 || nr_virtfn > iov->total_VFs ||
	    (!(iov->cap & PCI_SRIOV_CAP_VFM) && (nr_virtfn > initial)))
		return -EINVAL;
    ...
}

If an early exit occurs here, the hardware BAR remains inflated and
iov->num_VFs remains 0.

Because iov->num_VFs is 0, subsequent cleanup calls like pci_disable_sriov()
during driver teardown or system shutdown will bypass the restore logic due to
the early return in sriov_disable():

drivers/pci/iov.c:sriov_disable() {
	struct pci_sriov *iov = dev->sriov;

	if (!iov->num_VFs)
		return;
    ...
}

Will this leave the hardware BAR permanently inflated across kexec or warm
reboots, potentially leading to the MMIO space exhaustion this patch aims to
fix?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260505170010.3414074-1-marcin.bernatowicz@linux.intel.com?part=2