Re: Xen and Qemu virtio question

[Vikram Garhwal <vikram.garhwal@xxxxxxx>]

Hi Peng,
Please see my comments below.
On Wed, Jan 03, 2024 at 05:38:07AM +0000, Peng Fan wrote:
> Hi Vikram, Oleksii
> 
> I follow the slide virtio for Xen on ARM[1], but I met some issues, and
> stuck for about two days.
> 
> I use upstream lastest qemu repo master branch, not qemu-xen.git
> repo.
This is right.
> 
> My start command as below[2], but seems I need first `xl create domu.cfg`,
> otherwise it will fail, because xen hypervisor
> dm_op->rcu_lock_remote_domain_by_id will return failure if domu
> not created.  My domu cfg is simple:
> kernel = "/run/media/boot-mmcblk1p1/Image"
> disk = [ '/etc/xen/disk_1.img,,xvda,specification=virtio' ]
> cmdline = "console=hvc0 root=/dev/xvda rw"
> name = "DomU"
> memory = 512
> serial = "pty"
> 
> I drop qdisk in the disk entry, because xen tool report qdisk and virtio
> not compatible.
> 
> And the arg xen_domid should be same as domu domain id? Is
> there any dynamic way to set xen_domid, start qemu when start
> domu?
Yes, it should be xen_domid. Below virtio-disk patches will take care of
invoking QEMU with right domid.
> 
> Does the domu dts still needed to include the virtio,mmio node?
> 
> however xl create domu.cfg relies virtio disk ready, which needs qemu
> start first. This confuses me. How do you address this
> or I do something wrong?
> 
> Then after xl create,  I quickly start qemu, but met:
> failed to create ioreq server, then I see there is mismatch.
> qemu use HVM_IOREQSRV_BUFIOREQ_ATOMIC to create ioreq server,
> but xen ioreq_server_create will return failure:
>      if ( !IS_ENABLED(CONFIG_X86) && bufioreq_handling )                      
>                        
>                return -EINVAL;
> 
There is a downstream patch for this:
https://github.com/Xilinx/xen/commit/be35b46e907c7c78fd23888d837475eb28334638

> So I change HVM_IOREQSRV_BUFIOREQ_OFF in qemu, but met:
> qemu-system-aarch64: failed to map ioreq server resources: error 2
> handle=0xaaaad26c7f30
> qemu-system-aarch64: xen hardware virtual machine initialisation failed
> 
> Do you have out of box repo that works well? Including Qemu and Xen,
> I am trying virtio disk, but will move to test virtio gpu soon.
> 
> I am not sure there are some downstream patches in your side to
> address and make it work well.
> 
We have a few downstream patches for xen-tools. 
For Virtio disk backend:
https://github.com/Xilinx/xen/commit/947280803294bbb963f428423f679d074c60d632
For Virtio-net:
https://github.com/Xilinx/xen/commit/32fcc702718591270e5c8928b7687d853249c882
For changing the machine name to Xenpvh(to align with QEMU changes):
https://github.com/Xilinx/xen/commit/5f669949c9ffdb1947cb47038956b5fb8eeb072a

With above 4 patches it should work for you. Please re-compile Xen and Xen-tools
first and finally compile QEMU with this Xen.

> Thanks for your help.
> 
> Thanks,
> Peng.
> 
> [1]https://www.youtube.com/watch?v=boRQ8UHc760
> 
> [2]qemu-system-aarch64  -xen-domid 1 \
> -chardev socket,id=libxl-cmd,path=qmp-libxl-1,server=on,wait=off \
> -mon chardev=libxl-cmd,mode=control \
> -chardev socket,id=libxenstat-cmd,path=qmp-libxenstat-1,server=on,wait=off \
> -mon chardev=libxenstat-cmd,mode=control \
> -xen-attach -name guest0 -vnc none -display none -nographic \
> -machine xenpvh -m 513 &