Re: [PATCH v1] PCI: Add support for ACS Enhanced Capability

[Jason Gunthorpe]

On Tue, Jan 20, 2026 at 02:11:30AM +0800, Wei Wang wrote:
> Add support for the ACS (Access Control Services) Enhanced Capability,
> introduced with PCIe Gen 5. These new configuration options can be
> controlled via the config_acs= boot parameter.
> 
> By default, the ACS Unclaimed Request Redirect Control (URRC) bit is
> enabled if supported by the hardware (i.e., if the ACS Enhanced Capability
> is present). This setting is particularly important for device passthrough
> in virtualization scenarios.

The memory target access bits should be set to request redirect as
well. Linux's grouping logic effectively has assumed the enabled behavior
forever.

Jason