Re: [PATCH v3 1/2] PCI: Enable the enhanced ACS controls introduced by PCI_ACS_ECAP

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Feb 02, 2026 at 07:33:34PM +0800, Wei Wang wrote:
> The ACS Enhanced Capability introduces several new access controls to
> improve device isolation. These new controls are particularly important
> for device passthrough in virtualization scenarios.
> 
> For example, a DMA transaction from a device may target a guest physical
> address that lies within the memory aperture of the switch's upstream
> port, but not within any memory aperture or BAR space of a downstream
> port. In such cases, the switch would generate an Unsupported Request (UR)
> response to the device, which is undesirable. Enabling Unclaimed Request
> Redirect Control ensures that these DMA requests are forwarded upstream
> instead of being rejected.
> 
> The ACS DSP and USP Memory Target Access Control and ACS I/O Request
> Blocking features similarly enhance device isolation. Device grouping in
> Linux assumes that devices are properly isolated. Therefore, enable these
> controls by default if PCI_ACS_ECAP is supported by the hardware. As with
> other basic ACS access controls, these new controls can be configured via
> the config_acs= boot parameter.
> 
> Signed-off-by: Wei Wang <wei.w.wang@hotmail.com>
> ---
>  .../admin-guide/kernel-parameters.txt         | 23 +++++++++++++------
>  drivers/pci/pci.c                             | 13 ++++++++++-
>  include/uapi/linux/pci_regs.h                 |  7 ++++++
>  3 files changed, 35 insertions(+), 8 deletions(-)

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

Jason