Re: Testing the virtio-vhost-user QEMU patch

[Alyssa Ross <hi@alyssa.is>]

Stefan Hajnoczi <stefanha@redhat.com> writes:

> On Tue, Jul 21, 2020 at 07:14:38AM +0000, Alyssa Ross wrote:
>> Hi -- I hope it's okay me reaching out like this.
>> 
>> I've been trying to test out the virtio-vhost-user implementation that's
>> been posted to this list a couple of times, but have been unable to get
>> it to boot a kernel following the steps listed either on
>> <https://wiki.qemu.org/Features/VirtioVhostUser> or
>> <https://ndragazis.github.io/dpdk-vhost-vvu-demo.html>.
>> 
>> Specifically, the kernel appears to be unable to write to the
>> virtio-vhost-user device's PCI registers.  I've included the full panic
>> output from the kernel at the end of this message.  The panic is
>> reproducible with two different kernels I tried (with different configs
>> and versions).  I tried both versions of the virtio-vhost-user I was
>> able to find[1][2], and both exhibited the same behaviour.
>> 
>> Is this a known issue?  Am I doing something wrong?
>
> Hi,
> Unfortunately I'm not sure what the issue is. This is an early
> virtio-pci register access before a driver for any specific device type
> (net, blk, vhost-user, etc) comes into play.

Small update here: I tried on another computer, and it worked.  Made
sure that it was exactly the same QEMU binary, command line, and VM
disk/initrd/kernel, so I think I can fairly confidently say the panic
depends on what hardware QEMU is running on.  I set -cpu value to the
same on both as well (SandyBridge).

I also discovered that it works on my primary computer (the one it
panicked on before) with KVM disabled.

Note that I've only got so far as finding that it boots on the other
machine -- I haven't verified yet that it actually works.

Bad host CPU:  Intel(R) Core(TM) i5-2520M CPU @ 2.50GHz
Good host CPU: AMD EPYC 7401P 24-Core Processor

May I ask what host CPUs other people have tested this on?  Having more
data would probably be useful.  Could it be an AMD vs. Intel thing?