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

[Wei Wang]

On 1/21/26 12:41 AM, Jason Gunthorpe wrote:
> 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.
Yes, sounds good, thanks.
I think the REQ_ACS_FLAGS also needs to include the check.