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

[Sergio Lopez]

Jing Liu <address@hidden> writes:

> Hi Sergio,
>
> On 8/29/2019 11:46 PM, Sergio Lopez wrote:
>>
>> Jing Liu <address@hidden> 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?

The kernel config I posted lacks support for DOS partitions. Adding
CONFIG_MSDOS_PARTITION=y should allow you to boot from /dev/vda3.

Anyway, in case you also want to try booting from /dev/vda (without
partitions), this is the recipe I use to quickly create a minimal rootfs
image:

# wget 
http://dl-cdn.alpinelinux.org/alpine/v3.10/releases/x86_64/alpine-minirootfs-3.10.2-x86_64.tar.gz
# qemu-img create -f raw alpine-rootfs-x86_64.raw 1G
# sudo losetup /dev/loop0 alpine-rootfs-x86_64.raw
# sudo mkfs.ext4 /dev/loop0
# sudo mount /dev/loop0 /mnt
# sudo tar xpf alpine-minirootfs-3.10.2-x86_64.tar.gz -C /mnt
# sudo umount /mnt
# sudo losetup -d /dev/loop0

The rootfs will be missing openrc, so you'll need to add "init=/bin/sh"
to the command line.

Sergio.

> 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
>>>>
>>

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