[SRU][P:gcp][PATCH 0/2] NVIDIA Grace update for Google (Sep 2025)

[Tim Whisonant]

BugLink: https://bugs.launchpad.net/bugs/2126453

SRU Justification:

[Impact]

iommu: Skip PASID validation for devices without PASID capability

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.


UBUNTU: [Packaging] gcp: disable CONFIG_IOMMU_DEFAULT_DMA_STRICT enable CONFIG_IOMMU_DEFAULT_DMA_LAZY

NVIDIA Grace platform recommends this setting as
of the 25 Sep 2025 list of configs found at [1].

[1] https://docs.nvidia.com/grace/patches-config-guide/platform-software-patches-config.html

[Fix]

This patchset targets plucky:linux-gcp.

[Test Plan]

Boot tested and minimal Grace checkout.
Google to perform verification once platform is available.

[Where problems could occur]

The changes affect the iommu.

Tim Whisonant (1):
  UBUNTU: [Packaging] gcp: disable CONFIG_IOMMU_DEFAULT_DMA_STRICT
    enable CONFIG_IOMMU_DEFAULT_DMA_LAZY

Tushar Dave (1):
  iommu: Skip PASID validation for devices without PASID capability

 debian.gcp/config/annotations |  6 ++++++
 drivers/iommu/iommu.c         | 27 +++++++++++++++++++--------
 2 files changed, 25 insertions(+), 8 deletions(-)

-- 
2.43.0