linux-kernel - Re: [PATCH v12 04/17] PCI: Enable PASID only when ACS RR & UF enabled on upstream path

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Date:   Fri, 26 Aug 2022 11:26:26 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     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>,
        Fenghua Yu <fenghua.yu@...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 v12 04/17] PCI: Enable PASID only when ACS RR & UF
 enabled on upstream path

On Fri, Aug 26, 2022 at 08:11:28PM +0800, Lu Baolu wrote:
> The Requester ID/Process Address Space ID (PASID) combination
> identifies an address space distinct from the PCI bus address space,
> e.g., an address space defined by an IOMMU.
> 
> But the PCIe fabric routes Memory Requests based on the TLP address,
> ignoring any PASID (PCIe r6.0, sec 2.2.10.4), so a TLP with PASID that
> SHOULD go upstream to the IOMMU may instead be routed as a P2P
> Request if its address falls in a bridge window.
> 
> To ensure that all Memory Requests with PASID are routed upstream,
> only enable PASID if ACS P2P Request Redirect and Upstream Forwarding
> are enabled for the path leading to the device.
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Suggested-by: Kevin Tian <kevin.tian@...el.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> Tested-by: Tony Zhu <tony.zhu@...el.com>
> ---
>  drivers/pci/ats.c | 3 +++
>  1 file changed, 3 insertions(+)

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

Jason