Re: [PATCH v5 6/7] iommu/vt-d: Fail probe on ATS configuration failure

[Baolu Lu]

On 5/29/26 04:23, Pranjal Shrivastava wrote:
> Update the Intel VT-d driver to handle ATS configuration and enablement
> more strictly. Specifically, update the device probe to fail if
> pci_prepare_ats() returns an error. This ensures that any ATS-capable
> master reaching the attach phase is guaranteed to have a valid config.
>
> Additionally, update iommu_enable_pci_ats() to WARN() if pci_enable_ats
> fails. Since earlier checks in the probe phase preclude config-related
> failures, any failure during hardware enablement is considered a kernel
> bug.
>
> Signed-off-by: Pranjal Shrivastava <praan@xxxxxxxxxx>
> ---
>   drivers/iommu/intel/iommu.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index ed6d3a0203f5..f13da16717fe 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -876,8 +876,14 @@ static void iommu_enable_pci_ats(struct device_domain_info *info)
>   	if (!pci_ats_page_aligned(pdev))
>   		return;
>   
> -	if (!pci_enable_ats(pdev, VTD_PAGE_SHIFT))
> -		info->ats_enabled = 1;
> +	/*
> +	 * pci_enable_ats() should not fail here because earlier checks
> +	 * have already verified support and configuration.
> +	 */
> +	if (WARN_ON(pci_enable_ats(pdev, VTD_PAGE_SHIFT)))
> +		return;
> +
> +	info->ats_enabled = 1;
>   }
>   
>   static void iommu_disable_pci_ats(struct device_domain_info *info)
> @@ -3292,7 +3298,10 @@ static struct iommu_device *intel_iommu_probe_device(struct device *dev)
>   
>   	dev_iommu_priv_set(dev, info);
>   	if (pdev && pci_ats_supported(pdev)) {
> -		pci_prepare_ats(pdev, VTD_PAGE_SHIFT);
> +		ret = pci_prepare_ats(pdev, VTD_PAGE_SHIFT);
> +		if (ret)
> +			goto free;
> +
>   		ret = device_rbtree_insert(iommu, info);
>   		if (ret)
>   			goto free;

Sashiko made a valuable review comment, and I believe it applies here as
well:

[Severity: High]
Since ATS is an optional performance optimization, does failing the
IOMMU probe when pci_prepare_ats() fails break backward compatibility?

This completely prevents devices with buggy ATS capabilities (or VF/PF
STU mismatches) from attaching to the IOMMU.

Could this disable DMA translation entirely for hardware that would
otherwise work correctly without ATS?

Thanks,
baolu