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Re: [RFC][PATCH 0/3] IVSHMEM version 2 device for QEMU

From: Jan Kiszka
Subject: Re: [RFC][PATCH 0/3] IVSHMEM version 2 device for QEMU
Date: Mon, 2 Dec 2019 07:16:57 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1

On 27.11.19 18:19, Jan Kiszka wrote:
Hi Liang,

On 27.11.19 16:28, Liang Yan wrote:

On 11/11/19 7:57 AM, Jan Kiszka wrote:
To get the ball rolling after my presentation of the topic at KVM Forum
[1] and many fruitful discussions around it, this is a first concrete
code series. As discussed, I'm starting with the IVSHMEM implementation
of a QEMU device and server. It's RFC because, besides specification and
implementation details, there will still be some decisions needed about
how to integrate the new version best into the existing code bases.

If you want to play with this, the basic setup of the shared memory
device is described in patch 1 and 3. UIO driver and also the
virtio-ivshmem prototype can be found at


Accessing the device via UIO is trivial enough. If you want to use it
for virtio, this is additionally to the description in patch 3 needed on
the virtio console backend side:

     modprobe uio_ivshmem
     echo "1af4 1110 1af4 1100 ffc003 ffffff" > /sys/bus/pci/drivers/uio_ivshmem/new_id
     linux/tools/virtio/virtio-ivshmem-console /dev/uio0

And for virtio block:

     echo "1af4 1110 1af4 1100 ffc002 ffffff" > /sys/bus/pci/drivers/uio_ivshmem/new_id      linux/tools/virtio/virtio-ivshmem-console /dev/uio0 /path/to/disk.img

After that, you can start the QEMU frontend instance with the
virtio-ivshmem driver installed which can use the new /dev/hvc* or
/dev/vda* as usual.

Any feedback welcome!

Hi, Jan,

I have been playing your code for last few weeks, mostly study and test,
of course. Really nice work. I have a few questions here:

First, qemu part looks good, I tried test between couple VMs, and device
could pop up correctly for all of them, but I had some problems when
trying load driver. For example, if set up two VMs, vm1 and vm2, start
ivshmem server as you suggested. vm1 could load uio_ivshmem and
virtio_ivshmem correctly, vm2 could load uio_ivshmem but could not show
up "/dev/uio0", virtio_ivshmem could not be loaded at all, these still
exist even I switch the load sequence of vm1 and vm2, and sometimes
reset "virtio_ivshmem" could crash both vm1 and vm2. Not quite sure this
is bug or "Ivshmem Mode" issue, but I went through ivshmem-server code,
did not related information.

If we are only talking about one ivshmem link and vm1 is the master, there is not role for virtio_ivshmem on it as backend. That is purely a frontend driver. Vice versa for vm2: If you want to use its ivshmem instance as virtio frontend, uio_ivshmem plays no role.

The "crash" is would be interesting to understand: Do you see kernel panics of the guests? Or are they stuck? Or are the QEMU instances stuck? Do you know that you can debug the guest kernels via gdb (and gdb-scripts of the kernel)?

I started some code work recently, such as fix code style issues and
some work based on above testing, however I know you are also working on
RFC V2, beside the protocol between server-client and client-client is
not finalized yet either, things may change, so much appreciate if you
could squeeze me into your develop schedule and share with me some
plans, :-)  Maybe I could send some pull request in your github repo?

I'm currently working on a refresh of the Jailhouse queue and the kernel patches to incorporate just two smaller changes:

  - use Siemens device ID
  - drop "features" register from ivshmem device

I have not yet touched the QEMU code for that so far, thus no conflict yet. I would wait for your patches then.

If it helps us to work on this together, I can push things to github as well. Will drop you a note when done. We should just present the outcome frequently as new series to the list.

I've updated my queues, mostly small changes, mostly to the kernel bits. Besides the already announced places, you can also find them as PR targets on


To give the whole thing broader coverage, I will now also move forward and integrate the current state into Jailhouse - at the risk of having to rework the interface there once again. But there are a number of users already requiring the extended features (or even using them), plus this gives a nice test coverage of key components and properties.


Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux

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