[PATCH 6.12] iommu: Skip PASID validation for devices without PASID capability

[PATCH 6.12] iommu: Skip PASID validation for devices without PASID capability

[Dmitrii Chervov]

From: Tushar Dave <tdave@nvidia.com>

[ Upstream commit b3f6fcd8404f9f92262303369bb877ec5d188a81 ]

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>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Link: https://lore.kernel.org/r/20250520011937.3230557-1-tdave@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

[ Refactored to apply cleanly without support attaching PASID to the blocked domain ]
Signed-off-by: Dmitrii Chervov <fary.ru@gmail.com>
---
My greeting to you LTS maintainers! This is my first kernel patch.
I did a manual backport because cherry-pick failed (6.12 LTS did not have
this series: https://lore.kernel.org/all/20241204122928.11987-1-yi.l.liu@intel.com/).
This patch is tremendously helpful for Nvidia Grace servers. Without it
their GPU direct technology did not work.

 kdrivers/iommu/iommu.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 0ad55649e2d0..62e1d6372503 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -3341,9 +3341,11 @@ 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);
-		if (ret)
-			goto err_revert;
+		if (device->dev->iommu->max_pasids > 0) {
+			ret = domain->ops->set_dev_pasid(domain, device->dev, pasid);
+			if (ret)
+				goto err_revert;
+		}
 	}
 
 	return 0;
@@ -3355,7 +3357,8 @@ static int __iommu_set_group_pasid(struct iommu_domain *domain,
 
 		if (device == last_gdev)
 			break;
-		ops->remove_dev_pasid(device->dev, pasid, domain);
+		if (device->dev->iommu->max_pasids > 0)
+			ops->remove_dev_pasid(device->dev, pasid, domain);
 	}
 	return ret;
 }
@@ -3368,8 +3371,10 @@ static void __iommu_remove_group_pasid(struct iommu_group *group,
 	const struct iommu_ops *ops;
 
 	for_each_group_device(group, device) {
-		ops = dev_iommu_ops(device->dev);
-		ops->remove_dev_pasid(device->dev, pasid, domain);
+		if (device->dev->iommu->max_pasids > 0) {
+			ops = dev_iommu_ops(device->dev);
+			ops->remove_dev_pasid(device->dev, pasid, domain);
+		}
 	}
 }
 
@@ -3403,7 +3408,13 @@ int iommu_attach_device_pasid(struct iommu_domain *domain,
 
 	mutex_lock(&group->mutex);
 	for_each_group_device(group, device) {
-		if (pasid >= device->dev->iommu->max_pasids) {
+		/*
+		 * Skip PASID validation for devices without PASID support
+		 * (max_pasids = 0). These devices cannot issue transactions
+		 * with PASID, so they don't affect group's PASID usage.
+		 */
+		if ((device->dev->iommu->max_pasids > 0) &&
+		    (pasid >= device->dev->iommu->max_pasids)) {
 			ret = -EINVAL;
 			goto out_unlock;
 		}
-- 
2.43.0

Re: [PATCH 6.12] iommu: Skip PASID validation for devices without PASID capability

[Sasha Levin]

Queued for 6.12, thanks.

-- 
Thanks,
Sasha