linux-kernel - Re: [PATCH v11 04/13] PCI: Allow PASID only when ACS enforced on upstreaming path

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Message-ID: <Yv1wVfCWHnTdvPOc@nvidia.com>
Date:   Wed, 17 Aug 2022 19:48:53 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 04/13] PCI: Allow PASID only when ACS enforced on
 upstreaming path

On Wed, Aug 17, 2022 at 04:17:43PM -0500, Bjorn Helgaas wrote:

> Does the PCIe spec really allow TLPs with PASID to be routed anywhere
> except upstream?

I think yes:

 2.2.10.2 End-End TLP Prefix Processing:

 The presence of an End-End TLP Prefix does not alter the routing of a
 TLP. TLPs are routed based on the routing rules covered in Section
 2.2.4 .

Which I read as saying that routing is done after stripping all the
prefixes. PASID is a prefix.

Lu, you may want to quote the spec in the commit message to make it
clear.

A strange choice in my opinion, but there it is..

Jason