linux-kernel - Re: [RFC] Proposal of QEMU PCI Endpoint test environment

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Message-ID: <a24e048b-c1a2-78fe-9cd2-a5967e566a73@igel.co.jp>
Date:   Fri, 25 Aug 2023 17:56:53 +0900
From:   Shunsuke Mie <mie@...l.co.jp>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Marcel Apfelbaum <marcel.apfelbaum@...il.com>,
        qemu-devel@...gnu.org, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org,
        Krzysztof Wilczyński <kw@...ux.com>,
        Kishon Vijay Abraham I <kishon@...nel.org>
Subject: Re: [RFC] Proposal of QEMU PCI Endpoint test environment


On 2023/08/23 15:09, Manivannan Sadhasivam wrote:
> On Fri, Aug 18, 2023 at 10:46:02PM +0900, Shunsuke Mie wrote:
>> Hi all,
>>
>> We are proposing to add a new test syste to Linux for PCIe Endpoint. That
>> can be run on QEMU without real hardware. At present, partially we have
>> confirmed that pci-epf-test is working, but it is not yet complete.
>> However, we would appreciate your comments on the architecture design.
>>
>> # Background
>> The background is as follows.
>>
>> PCI Endpoint function driver is implemented using the PCIe Endpoint
>> framework, but it requires physical boards for testing, and it is difficult
>> to test sufficiently. In order to find bugs and hardware-dependent
>> implementations early, continuous testing is required. Since it is
>> difficult to automate tests that require hardware, this RFC proposes a
>> virtual environment for testing PCI endpoint function drivers.
>>
> This sounds exciting to me and yes, it is going to be really helpful for
> validating EP framework as a whole.
>
>> # Architecture
>> The overview of the architecture is as follows.
>>
>>    Guest 1                        Guest 2
>> +-------------------------+    +----------------------------+
>> | Linux kernel            |    | Linux kernel               |
>> |                         |    |                            |
>> | PCI EP function driver  |    |                            |
>> | (e.g. pci-epf-test)     |    |                            |
>> |-------------------------|    | PCI Device Driver          |
>> | (2) QEMU EPC Driver     |    | (e.g. pci_endpoint_test)   |
>> +-------------------------+    +----------------------------+
>> +-------------------------+    +----------------------------+
>> | QEMU                    |    | QEMU                       |
>> |-------------------------|    |----------------------------|
>> | (1) QEMU PCI EPC Device *----* (3) QEMU EPF Bridge Device |
>> +-------------------------+    +----------------------------+
>>
>> At present, it is designed to work guests only on the same host, and
>> communication is done through Unix domain sockets.
>>
>> The three parts shown in the figure were introduced this time.
>>
>> (1) QEMU PCI Endpoint Controller(EPC) Device
>> PCI Endpoint Controller implemented as QEMU PCI device.
>> (2) QEMU PCI Endpoint Controller(EPC) Driver
>> Linux kernel driver that drives the device (1). It registers a epc device
>> to linux kernel and handling each operations for the epc device.
>> (3) QEMU PCI Endpoint function(EPF) Bridge Device
>> QEMU PCI device that cooperates with (1) and performs accesses to pci
>> configuration space, BAR and memory space to communicate each guests, and
>> generates interruptions to the guest 1.
>>
> I'm not very familiar with Qemu, but why can't the existing Qemu PCIe host
> controller devices used for EP communication? I mean, what is the need for a
> dedicated EPF bridge device (3) in host? (Guest 2 as per your diagram).
>
> Is that because you use socket communication between EP and host?

At least, the part that communicates with (1) is necessary, but I don't 
know if
the current implementation is appropriate. In addition, there is a 
performance
issue, so I am currently investigating QEMU more. e.g. pci emulation, 
shared-memory, etc.

I'd like to improve and submit a next rfc.

Thanks,

Shunsuke Mie

> - Mani
>
>> Each projects are:
>> (1), (3) https://github.com/ShunsukeMie/qemu/tree/epf-bridge/v1
>> files: hw/misc/{qemu-epc.{c,h}, epf-bridge.c}
>> (2) https://github.com/ShunsukeMie/linux-virtio-rdma/tree/qemu-epc
>> files: drivers/pci/controller/pcie-qemu-ep.c
>>
>> # Protocol
>>
>> PCI, PCIe has a layer structure that includes Physical, Data Lane and
>> Transaction. The communicates between the bridge(3) and controller (1)
>> mimic the Transaction. Specifically, a protocol is implemented for
>> exchanging fd for communication protocol version check and communication,
>> in addition to the interaction equivalent to PCIe Transaction Layer Packet
>> (Read and Write of I/O, Memory, Configuration space and Message). In my
>> mind, we need to discuss the communication mor.
>>
>> We also are planning to post the patch set after the code is organized and
>> the protocol discussion is matured.
>>
>> Best regards,
>> Shunsuke