[SRU][O/N][PATCH 0/3] Backport pci=config_acs parameter with fix commit

[Jacob Martin]

BugLink: https://bugs.launchpad.net/bugs/2100340

SRU Justification:

[Impact]

The PCI ACS capability parameter is used to enable and configure access
control between PCIe devices. In particular, this parameter can enable
and/or restrict peer-to-peer traffic between so-configured PCIe devices.

For example, this parameter is necessary for GPUDirect RDMA
applications, where peer-to-peer communication between a GPU and an
RDMA-capable device is required. This parameter allows an administrator
to configure the system for the specific level of isolation between PCIe
devices required to enable this feature for their use case.

[Fix]

For Oracular, this consists of a clean cherry pick from mainline of
commit 9cf8a952d57b ("PCI/ACS: Fix 'pci=config_acs=' parameter") to fix
the functionality of the config_acs parameter introduced by commit
47c8846a49ba ("PCI: Extend ACS configurability").

For Noble, this consists of clean cherry picks of commits 47c8846a49ba
("PCI: Extend ACS configurability") and 9cf8a952d57b ("PCI/ACS: Fix
'pci=config_acs=' parameter").

[Test Plan]

The Noble and Oracular patchsets were tested on a DGX GH200 system by
booting with the kernel parameter test cases described in the commit
message of 9cf8a952d57b ("PCI/ACS: Fix 'pci=config_acs=' parameter").

Multiple PCIe devices could be configured with the pci=config_acs
parameter as is expected with the fix commit, and pci=disable_acs_redir
works as expected.

[Where problems could occur]

This affects the pci=config_acs and pci=config_acs_redir kernel boot
parameters. Issues could arise as malfunctioning of these two boot
parameters, or as improper configuration of PCIe devices.

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2.43.0