Re: [PATCH v2 12/13] PCI/P2PDMA: Add KUnit coverage for the ACS P2P routing walk

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] pci_p2pdma_release() skips synchronize_rcu() when p2pdma->pool is NULL, leading to a Use-After-Free of the pci_p2pdma struct and its XArray inside RCU read-side critical sections.
--

--- Patch [12]: [PATCH v2 12/13] PCI/P2PDMA: Add KUnit coverage for the ACS P2P routing walk ---
commit c4a68b62f4ec894cc35240eda46bf42dc5f562d9
Author: Leon Romanovsky <leon@kernel.org>

PCI/P2PDMA: Add KUnit coverage for the ACS P2P routing walk

Extend the ACS KUnit suite with end-to-end coverage of
calc_map_type_and_dist(), the provider-to-client hierarchy walk.

> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index c7680964d8a64..18e5339bc49e9 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
[ ... ]
> @@ -859,6 +859,7 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client,
>  	rcu_read_unlock();
>  	return map_type;
>  }
> +EXPORT_SYMBOL_IF_KUNIT(calc_map_type_and_dist);

[Severity: High]
This is a pre-existing issue, but does this code have a race condition
leading to a use-after-free when interacting with pci_p2pdma_release()?

If a device acts as a P2PDMA provider without setting up an allocator pool
(for example, via vfio-pci or mlx5), pci_p2pdma_release() skips
synchronize_rcu() because p2pdma->pool is NULL:

drivers/pci/p2pdma.c:pci_p2pdma_release() {
        ...
        if (p2pdma->pool)
                synchronize_rcu();
        ...
}

When the provider driver is unbound, devres frees the pci_p2pdma structure
and destroys the XArray. Concurrently, calc_map_type_and_dist() executing
here inside its RCU read-side critical section can dereference the freed
p2pdma pointer and call xa_store() on the destroyed XArray.

Should synchronize_rcu() be called during release regardless of whether
the allocator pool is set up?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260806-fix-p2p-acs-v2-0-0cec14812965@nvidia.com?part=12