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

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Message-ID:
 <SI2PR01MB4393709A1FFDD137DEBFA883DC96A@SI2PR01MB4393.apcprd01.prod.exchangelabs.com>
Date: Wed, 21 Jan 2026 17:18:46 +0800
From: Wei Wang <wei.w.wang@...mail.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: bhelgaas@...gle.com, akpm@...ux-foundation.org, bp@...en8.de,
 rdunlap@...radead.org, alex@...zbot.org, kevin.tian@...el.com,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v1] PCI: Add support for ACS Enhanced Capability

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.