# Xen PVH machine (`xenpvh`)

Xen supports a spectrum of types of guests that vary in how they depend on HW virtualization features, emulation models and paravirtualization. PVH is a mode that uses HW virtualization features (like HVM) but tries to avoid emulation models and instead use passthrough or paravirtualized devices.

QEMU can be used to provide PV virtio devices on an emulated PCIe controller. That is the purpose of this minimal machine.

## Supported devices

The x86 Xen PVH QEMU machine provide the following devices:

- RAM

- GPEX host bridge

- virtio-pci devices

The idea is to only connect virtio-pci devices but in theory any compatible PCI device model will work depending on Xen and guest support.

## Running

The Xen tools will typically construct a command-line and launch QEMU for you when needed. But here’s an example of what it can look like in case you need to construct one manually:

    qemu-system-i386 -xen-domid 3 -no-shutdown        \
      -chardev socket,id=libxl-cmd,path=/var/run/xen/qmp-libxl-3,server=on,wait=off \
      -mon chardev=libxl-cmd,mode=control             \
      -chardev socket,id=libxenstat-cmd,path=/var/run/xen/qmp-libxenstat-3,server=on,wait=off \
      -mon chardev=libxenstat-cmd,mode=control        \
      -nodefaults                                     \
      -no-user-config                                 \
      -xen-attach -name g0                            \
      -vnc none                                       \
      -display none                                   \
      -device virtio-net-pci,id=nic0,netdev=net0,mac=00:16:3e:5c:81:78 \
      -netdev type=tap,id=net0,ifname=vif3.0-emu,br=xenbr0,script=no,downscript=no \
      -smp 4,maxcpus=4                                \
      -nographic                                      \
      -machine xenpvh,ram-low-base=0,ram-low-size=2147483648,ram-high-base=4294967296,ram-high-size=2147483648,pci-ecam-base=824633720832,pci-ecam-size=268435456,pci-mmio-base=4026531840,pci-mmio-size=33554432,pci-mmio-high-base=824902156288,pci-mmio-high-size=68719476736 \
      -m 4096