Re: [PATCH v4 rc] iommu: Skip PASID validation for devices without PASID capability

[Baolu Lu <baolu.lu@linux.intel.com>]

On 5/20/2025 9:19 AM, Tushar Dave wrote:
> Generally PASID support requires ACS settings that usually create
> single device groups, but there are some niche cases where we can get
> multi-device groups and still have working PASID support. The primary
> issue is that PCI switches are not required to treat PASID tagged TLPs
> specially so appropriate ACS settings are required to route all TLPs to
> the host bridge if PASID is going to work properly.
> 
> pci_enable_pasid() does check that each device that will use PASID has
> the proper ACS settings to achieve this routing.
> 
> However, no-PASID devices can be combined with PASID capable devices
> within the same topology using non-uniform ACS settings. In this case
> the no-PASID devices may not have strict route to host ACS flags and
> end up being grouped with the PASID devices.
> 
> This configuration fails to allow use of the PASID within the iommu
> core code which wrongly checks if the no-PASID device supports PASID.
> 
> Fix this by ignoring no-PASID devices during the PASID validation. They
> will never issue a PASID TLP anyhow so they can be ignored.
> 
> Fixes: c404f55c26fc ("iommu: Validate the PASID in iommu_attach_device_pasid()")
> Cc:stable@vger.kernel.org
> Signed-off-by: Tushar Dave<tdave@nvidia.com>
> ---
> 
> changes in v4:
> - rebase to 6.15-rc7
> 
>   drivers/iommu/iommu.c | 43 ++++++++++++++++++++++++++++---------------
>   1 file changed, 28 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 4f91a740c15f..9d728800a862 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -3366,10 +3366,12 @@ static int __iommu_set_group_pasid(struct iommu_domain *domain,
>   	int ret;
>   
>   	for_each_group_device(group, device) {
> -		ret = domain->ops->set_dev_pasid(domain, device->dev,
> -						 pasid, old);
> -		if (ret)
> -			goto err_revert;
> +		if (device->dev->iommu->max_pasids > 0) {
> +			ret = domain->ops->set_dev_pasid(domain, device->dev,
> +							 pasid, old);
> +			if (ret)
> +				goto err_revert;
> +		}

You can save an indent by making it like this,

for_each_group_device(group, device) {
	if (device->dev->iommu->max_pasids == 0)
		continue;

	ret = domain->ops->set_dev_pasid(domain, device->dev, pasid, old);
	if (ret)
		goto err_revert;
}

Anyway,

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>