Re: [Qemu-devel] [PATCH v3 0/4] Introduce the microvm machine type

[Jing Liu <jing2.liu@linux.intel.com>]

Hi Sergio,

On 8/29/2019 11:46 PM, Sergio Lopez wrote:
> 
> Jing Liu <jing2.liu@linux.intel.com> writes:
> 
>> Hi Sergio,
>>
>> The idea is interesting and I tried to launch a guest by your
>> guide but seems failed to me. I tried both legacy and normal modes,
>> but the vncviewer connected and told me that:
>> The vm has no graphic display device.
>> All the screen in vnc is just black.
> 
> The microvm machine type doesn't support any graphics device, so you
> need to rely on the serial console.
Got it.

> 
>> kernel config:
>> CONFIG_KVM_MMIO=y
>> CONFIG_VIRTIO_MMIO=y
>>
>> I don't know if any specified kernel version/patch/config
>> is needed or anything I missed.
>> Could you kindly give some tips?
> 
> I'm testing it with upstream vanilla Linux. In addition to MMIO, you
> need to add support for PVH (the next version of this patchset, v4, will
> support booting from FW, so it'll be possible to use non-PVH ELF kernels
> and bzImages too).
> 
> I've just uploaded a working kernel config here:
> 
> https://gist.github.com/slp/1060ba3aaf708584572ad4109f28c8f9
> 
Thanks very much and this config is helpful to me.

> As for the QEMU command line, something like this should do the trick:
> 
> ./x86_64-softmmu/qemu-system-x86_64 -smp 1 -m 1g -enable-kvm -M microvm,legacy -kernel vmlinux -append "earlyprintk=ttyS0 console=ttyS0 reboot=k panic=1" -nodefaults -no-user-config -nographic -serial stdio
> 
> If this works, you can move to non-legacy mode with a virtio-console:
> 
> ./x86_64-softmmu/qemu-system-x86_64 -smp 1 -m 1g -enable-kvm -M microvm -kernel vmlinux -append "console=hvc0 reboot=k panic=1" -nodefaults -no-user-config -nographic -serial pty -chardev stdio,id=virtiocon0,server -device virtio-serial-device -device virtconsole,chardev=virtiocon0
> 
I tried the above two ways and it works now. Thanks!

> If is still working, you can try adding some devices too:
> 
> ./x86_64-softmmu/qemu-system-x86_64 -smp 1 -m 1g -enable-kvm -M microvm -kernel vmlinux -append "console=hvc0 reboot=k panic=1 root=/dev/vda" -nodefaults -no-user-config -nographic -serial pty -chardev stdio,id=virtiocon0,server -device virtio-serial-device -device virtconsole,chardev=virtiocon0 -netdev user,id=testnet -device virtio-net-device,netdev=testnet -drive id=test,file=alpine-rootfs-x86_64.raw,format=raw,if=none -device virtio-blk-device,drive=test
> 
But I'm wondering why the image I used can not be found.
root=/dev/vda3 and the same image worked well on normal qemu/guest-
config bootup, but didn't work here. The details are,

-append "console=hvc0 reboot=k panic=1 root=/dev/vda3 rw rootfstype=ext4" \

[    0.022784] Key type encrypted registered
[    0.022988] VFS: Cannot open root device "vda3" or 
unknown-block(254,3): error -6
[    0.023041] Please append a correct "root=" boot option; here are the 
available partitions:
[    0.023089] fe00         8946688 vda
[    0.023090]  driver: virtio_blk
[    0.023143] Kernel panic - not syncing: VFS: Unable to mount root fs 
on unknown-block(254,3)
[    0.023201] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.3.0-rc3 #23


BTW, root=/dev/vda is also tried and didn't work. The dmesg is a little 
different:

[    0.028050] Key type encrypted registered
[    0.028484] List of all partitions:
[    0.028529] fe00         8946688 vda
[    0.028529]  driver: virtio_blk
[    0.028615] No filesystem could mount root, tried:
[    0.028616]  ext4
[    0.028670]
[    0.028712] Kernel panic - not syncing: VFS: Unable to mount root fs 
on unknown-block(254,0)

I tried another ext4 img but still doesn't work.
Is there any limitation of blk image? Could I copy your image for simple
test?

Thanks in advance,
Jing

> Sergio.
> 
>> Thanks very much.
>> Jing
>>
>>
>>
>>> A QEMU instance with the microvm machine type can be invoked this way:
>>>
>>>    - Normal mode:
>>>
>>> qemu-system-x86_64 -M microvm -m 512m -smp 2 \
>>>    -kernel vmlinux -append "console=hvc0 root=/dev/vda" \
>>>    -nodefaults -no-user-config \
>>>    -chardev pty,id=virtiocon0,server \
>>>    -device virtio-serial-device \
>>>    -device virtconsole,chardev=virtiocon0 \
>>>    -drive id=test,file=test.img,format=raw,if=none \
>>>    -device virtio-blk-device,drive=test \
>>>    -netdev tap,id=tap0,script=no,downscript=no \
>>>    -device virtio-net-device,netdev=tap0
>>>
>>>    - Legacy mode:
>>>
>>> qemu-system-x86_64 -M microvm,legacy -m 512m -smp 2 \
>>>    -kernel vmlinux -append "console=ttyS0 root=/dev/vda" \
>>>    -nodefaults -no-user-config \
>>>    -drive id=test,file=test.img,format=raw,if=none \
>>>    -device virtio-blk-device,drive=test \
>>>    -netdev tap,id=tap0,script=no,downscript=no \
>>>    -device virtio-net-device,netdev=tap0 \
>>>    -serial stdio
>>>
>