Re: [PATCH v6 6/6] PCI: Add the enhanced ACS controls check to pci_acs_flags_enabled()

Jason Gunthorpe
2026-03-30T13:21:09Z

On Thu, Mar 12, 2026 at 05:06:37PM +0800, Wei Wang wrote:
> The enhanced ACS controls introduced by PCIe Gen 5 ensures better device
> isolation. On devices that support the PCI_ACS_ECAP capability, the
> controls are required to be enabled properly:
> - ACS I/O Request Blocking needs to be enabled to avoid unintended
> upstream I/O requests.
> - ACS DSP and USP Memory Target Access Control needs to be set with
> Request Redirect or Request Blocking to ensure the Downstream and
> Upstream Port memory resource ranges are not accessed by upstream
> memory requests.
> - ACS Unclaimed Request Redirect needs to be enabled to ensure accesses to
> areas that lies within a Switch's Upstream Port memory apertures but not
> within any Downstream Port memory apertures get redirected.
>
> To maintain compatibility with legacy devices that lack PCI_ACS_ECAP
> support, pci_acs_enabled() skips checking for the capability.

This seems conservative enough

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason