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

[Stefan Hajnoczi]

On Tue, Jul 02, 2019 at 02:11:02PM +0200, Sergio Lopez wrote:
> Microvm is a machine type inspired by both NEMU and Firecracker, and
> constructed after the machine model implemented by the latter.
> 
> It's main purpose is providing users a KVM-only machine type with fast
> boot times, minimal attack surface (measured as the number of IO ports
> and MMIO regions exposed to the Guest) and small footprint (specially
> when combined with the ongoing QEMU modularization effort).
> 
> Normally, other than the device support provided by KVM itself,
> microvm only supports virtio-mmio devices. Microvm also includes a
> legacy mode, which adds an ISA bus with a 16550A serial port, useful
> for being able to see the early boot kernel messages.
> 
> Microvm only supports booting PVH-enabled Linux ELF images. Booting
> other PVH-enabled kernels may be possible, but due to the lack of ACPI
> and firmware, we're relying on the command line for specifying the
> location of the virtio-mmio transports. If there's an interest on
> using this machine type with other kernels, we'll try to find some
> kind of middle ground solution.
> 
> This is the list of the exposed IO ports and MMIO regions when running
> in non-legacy mode:
> 
> address-space: memory
>     00000000d0000000-00000000d00001ff (prio 0, i/o): virtio-mmio
>     00000000d0000200-00000000d00003ff (prio 0, i/o): virtio-mmio
>     00000000d0000400-00000000d00005ff (prio 0, i/o): virtio-mmio
>     00000000d0000600-00000000d00007ff (prio 0, i/o): virtio-mmio
>     00000000d0000800-00000000d00009ff (prio 0, i/o): virtio-mmio
>     00000000d0000a00-00000000d0000bff (prio 0, i/o): virtio-mmio
>     00000000d0000c00-00000000d0000dff (prio 0, i/o): virtio-mmio
>     00000000d0000e00-00000000d0000fff (prio 0, i/o): virtio-mmio
>     00000000fee00000-00000000feefffff (prio 4096, i/o): kvm-apic-msi
> 
> address-space: I/O
>   0000000000000000-000000000000ffff (prio 0, i/o): io
>     0000000000000020-0000000000000021 (prio 0, i/o): kvm-pic
>     0000000000000040-0000000000000043 (prio 0, i/o): kvm-pit
>     000000000000007e-000000000000007f (prio 0, i/o): kvmvapic
>     00000000000000a0-00000000000000a1 (prio 0, i/o): kvm-pic
>     00000000000004d0-00000000000004d0 (prio 0, i/o): kvm-elcr
>     00000000000004d1-00000000000004d1 (prio 0, i/o): kvm-elcr
> 
> 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

Please post metrics that compare this against a minimal Q35.

With qboot it was later found that SeaBIOS can achieve comparable boot
times, so it wasn't worth maintaining qboot.

Data is needed to show that microvm is really a significant improvement
over a minimal Q35.

Stefan

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