Re: [PATCH 6/6] PCI/ATS: Mandate checking pci_ats_supported() before pci_prepare_ats()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Adding a WARN_ON() to pci_prepare_ats() causes spurious kernel warnings and potential panics because the ARM SMMUv3 driver does not check pci_ats_supported() prior to calling it.
--

commit eaccac64f7c8e00ef695d5c2076021c097520251
Author: Pranjal Shrivastava <praan@google.com>

PCI/ATS: Mandate checking pci_ats_supported() before pci_prepare_ats()

This commit updates pci_prepare_ats() to wrap the internal
pci_ats_supported() check in a WARN_ON(). It is intended to mandate that
all callers verify ATS support before calling the function.

> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -61,7 +63,7 @@ int pci_prepare_ats(struct pci_dev *dev, int ps)
>  {
>  	u16 ctrl;
>  
> -	if (!pci_ats_supported(dev))
> +	if (WARN_ON(!pci_ats_supported(dev)))

[Severity: High]
Will this trigger spurious warnings or panics for non-ATS PCI devices
on ARM systems?

The arm_smmu_probe_device() function appears to unconditionally invoke
pci_prepare_ats() for all PCI devices without verifying ATS support first:

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c:arm_smmu_probe_device() {
    ...
    if (dev_is_pci(dev)) {
        unsigned int stu = __ffs(smmu->pgsize_bitmap);

        pci_prepare_ats(to_pci_dev(dev), stu);
    }
    ...
}

Since this unpatched caller does not check pci_ats_supported() first, any
standard PCI device lacking ATS support might trigger this new WARN_ON()
during IOMMU device probe.

>  		return -EINVAL;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260601134204.2150602-1-praan@google.com?part=6