Messages in this thread | | | Date | Mon, 22 Aug 2022 15:43:18 +0800 | Subject | Re: [PATCH v11 04/13] PCI: Allow PASID only when ACS enforced on upstreaming path | From | Ethan Zhao <> |
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在 2022/8/19 7:00, Bjorn Helgaas 写道: > On Thu, Aug 18, 2022 at 07:53:15PM +0800, Baolu Lu wrote: >> On 2022/8/18 05:17, Bjorn Helgaas wrote: >>> On Wed, Aug 17, 2022 at 09:20:15AM +0800, Lu Baolu wrote: >>>> Some configurations of the PCI fabric will route device originated TLP >>>> packets based on the memory addresses. >>> This makes it sound like a few unusual configurations will route TLPs >>> based on memory addresses, but address routing is the default for all >>> PCIe Memory Requests, and ACS provides a way to override that default. >>> >>>> These configurations are incompatible with PASID as the PASID >>>> packets form a distinct address space. >>> I would say "the Requester ID/PASID combination forms a distinct >>> address space." >>> >>>> For instance, any configuration where switches are present >>>> without ACS enabled is incompatible. >>>> >>>> This enhances the pci_enable_pasid() interface by requiring the ACS to >>>> support Source Validation, Request Redirection, Completer Redirection, >>>> and Upstream Forwarding. This effectively means that devices cannot >>>> spoof their requester ID, requests and completions cannot be redirected, >>>> and all transactions are forwarded upstream, even as it passes through a >>>> bridge where the target device is downstream. >>> I think your patch actually requires all those features to be not just >>> "supported" but actually*enabled* for the entire path leading to the >>> device. >>> >>> To use the terms from the spec: >>> >>> "P2P Request Redirect" >>> "P2P Completion Redirect" >>> "Requester ID, Requests, and Completions" >>> >>> and maybe something like: >>> >>> ... even if the TLP looks like a P2P Request because its memory >>> address (ignoring the PASID) would fall in a bridge window and would >>> normally be routed downstream. >> Thank you for the suggestions. I will rephrase the commit message >> accordingly like this: >> >> >> PCI: Allow PASID only when ACS enforced on upstreaming path > PCI: Enable PASID only when ACS RR & UF enabled on upstream path > > 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.
Seeing these comments, my questions gone.
Thanks Bjorn !
>> The PCIe fabric routes TLPs based on memory addresses for all PCIe Memory >> Requests regardless of whether TLPs have PASID prefixes. This is stated in >> section "2.2.10.2 End-End TLP Prefix Processing" of the specification: >> >> 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 . >> >> As the Requester ID/PASID combination forms a distinct address space. The >> memory address based routing is not compatible for PASID TLPs anymore. >> Therefore we have to rely on ACS to override that default. >> >> This enhances pci_enable_pasid() interface by requiring the ACS features >> to be enabled for the entire path leading to the device. So that even if >> the TLP looks like a P2P Request because its memory address (ignoring the >> PASID) would fall in a bridge window and would normally be routed >> downstream. >> >> Best regards, >> baolu
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