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

Shunsuke Mie
2023-08-25T08:57:56Z

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