diff options
| -rw-r--r-- | MAINTAINERS | 2 | ||||
| -rw-r--r-- | docs/system/i386/xen.rst | 107 | ||||
| -rw-r--r-- | qemu-options.hx | 12 |
3 files changed, 90 insertions, 31 deletions
diff --git a/MAINTAINERS b/MAINTAINERS index 59b92ee640..fd6b362311 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -490,7 +490,7 @@ S: Supported F: include/sysemu/kvm_xen.h F: target/i386/kvm/xen* F: hw/i386/kvm/xen* -F: tests/avocado/xen_guest.py +F: tests/avocado/kvm_xen_guest.py Guest CPU Cores (other accelerators) ------------------------------------ diff --git a/docs/system/i386/xen.rst b/docs/system/i386/xen.rst index f06765e88c..81898768ba 100644 --- a/docs/system/i386/xen.rst +++ b/docs/system/i386/xen.rst @@ -15,46 +15,24 @@ Setup ----- Xen mode is enabled by setting the ``xen-version`` property of the KVM -accelerator, for example for Xen 4.10: +accelerator, for example for Xen 4.17: .. parsed-literal:: - |qemu_system| --accel kvm,xen-version=0x4000a,kernel-irqchip=split + |qemu_system| --accel kvm,xen-version=0x40011,kernel-irqchip=split Additionally, virtual APIC support can be advertised to the guest through the ``xen-vapic`` CPU flag: .. parsed-literal:: - |qemu_system| --accel kvm,xen-version=0x4000a,kernel-irqchip=split --cpu host,+xen_vapic + |qemu_system| --accel kvm,xen-version=0x40011,kernel-irqchip=split --cpu host,+xen-vapic When Xen support is enabled, QEMU changes hypervisor identification (CPUID 0x40000000..0x4000000A) to Xen. The KVM identification and features are not advertised to a Xen guest. If Hyper-V is also enabled, the Xen identification moves to leaves 0x40000100..0x4000010A. -The Xen platform device is enabled automatically for a Xen guest. This allows -a guest to unplug all emulated devices, in order to use Xen PV block and network -drivers instead. Under Xen, the boot disk is typically available both via IDE -emulation, and as a PV block device. Guest bootloaders typically use IDE to load -the guest kernel, which then unplugs the IDE and continues with the Xen PV block -device. - -This configuration can be achieved as follows - -.. parsed-literal:: - - |qemu_system| -M pc --accel kvm,xen-version=0x4000a,kernel-irqchip=split \\ - -drive file=${GUEST_IMAGE},if=none,id=disk,file.locking=off -device xen-disk,drive=disk,vdev=xvda \\ - -drive file=${GUEST_IMAGE},index=2,media=disk,file.locking=off,if=ide - -It is necessary to use the pc machine type, as the q35 machine uses AHCI instead -of legacy IDE, and AHCI disks are not unplugged through the Xen PV unplug -mechanism. - -VirtIO devices can also be used; Linux guests may need to be dissuaded from -umplugging them by adding 'xen_emul_unplug=never' on their command line. - Properties ---------- @@ -63,7 +41,10 @@ The following properties exist on the KVM accelerator object: ``xen-version`` This property contains the Xen version in ``XENVER_version`` form, with the major version in the top 16 bits and the minor version in the low 16 bits. - Setting this property enables the Xen guest support. + Setting this property enables the Xen guest support. If Xen version 4.5 or + greater is specified, the HVM leaf in Xen CPUID is populated. Xen version + 4.6 enables the vCPU ID in CPUID, and version 4.17 advertises vCPU upcall + vector support to the guest. ``xen-evtchn-max-pirq`` Xen PIRQs represent an emulated physical interrupt, either GSI or MSI, which @@ -83,8 +64,78 @@ The following properties exist on the KVM accelerator object: through simultaneous grants. For guests with large numbers of PV devices and high throughput, it may be desirable to increase this value. -OS requirements ---------------- +Xen paravirtual devices +----------------------- + +The Xen PCI platform device is enabled automatically for a Xen guest. This +allows a guest to unplug all emulated devices, in order to use paravirtual +block and network drivers instead. + +Those paravirtual Xen block, network (and console) devices can be created +through the command line, and/or hot-plugged. + +To provide a Xen console device, define a character device and then a device +of type ``xen-console`` to connect to it. For the Xen console equivalent of +the handy ``-serial mon:stdio`` option, for example: + +.. parsed-literal:: + -chardev stdio,mux=on,id=char0,signal=off -mon char0 \\ + -device xen-console,chardev=char0 + +The Xen network device is ``xen-net-device``, which becomes the default NIC +model for emulated Xen guests, meaning that just the default NIC provided +by QEMU should automatically work and present a Xen network device to the +guest. + +Disks can be configured with '``-drive file=${GUEST_IMAGE},if=xen``' and will +appear to the guest as ``xvda`` onwards. + +Under Xen, the boot disk is typically available both via IDE emulation, and +as a PV block device. Guest bootloaders typically use IDE to load the guest +kernel, which then unplugs the IDE and continues with the Xen PV block device. + +This configuration can be achieved as follows: + +.. parsed-literal:: + + |qemu_system| --accel kvm,xen-version=0x40011,kernel-irqchip=split \\ + -drive file=${GUEST_IMAGE},if=xen \\ + -drive file=${GUEST_IMAGE},file.locking=off,if=ide + +VirtIO devices can also be used; Linux guests may need to be dissuaded from +umplugging them by adding '``xen_emul_unplug=never``' on their command line. + +Booting Xen PV guests +--------------------- + +Booting PV guest kernels is possible by using the Xen PV shim (a version of Xen +itself, designed to run inside a Xen HVM guest and provide memory management +services for one guest alone). + +The Xen binary is provided as the ``-kernel`` and the guest kernel itself (or +PV Grub image) as the ``-initrd`` image, which actually just means the first +multiboot "module". For example: + +.. parsed-literal:: + + |qemu_system| --accel kvm,xen-version=0x40011,kernel-irqchip=split \\ + -chardev stdio,id=char0 -device xen-console,chardev=char0 \\ + -display none -m 1G -kernel xen -initrd bzImage \\ + -append "pv-shim console=xen,pv -- console=hvc0 root=/dev/xvda1" \\ + -drive file=${GUEST_IMAGE},if=xen + +The Xen image must be built with the ``CONFIG_XEN_GUEST`` and ``CONFIG_PV_SHIM`` +options, and as of Xen 4.17, Xen's PV shim mode does not support using a serial +port; it must have a Xen console or it will panic. + +The example above provides the guest kernel command line after a separator +(" ``--`` ") on the Xen command line, and does not provide the guest kernel +with an actual initramfs, which would need to listed as a second multiboot +module. For more complicated alternatives, see the command line +documentation for the ``-initrd`` option. + +Host OS requirements +-------------------- The minimal Xen support in the KVM accelerator requires the host to be running Linux v5.12 or newer. Later versions add optimisations: Linux v5.17 added diff --git a/qemu-options.hx b/qemu-options.hx index 7809036d8c..3eee3c33eb 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -3986,14 +3986,22 @@ ERST DEF("initrd", HAS_ARG, QEMU_OPTION_initrd, \ "-initrd file use 'file' as initial ram disk\n", QEMU_ARCH_ALL) SRST + ``-initrd file`` Use file as initial ram disk. ``-initrd "file1 arg=foo,file2"`` This syntax is only available with multiboot. - Use file1 and file2 as modules and pass arg=foo as parameter to the - first module. + Use file1 and file2 as modules and pass ``arg=foo`` as parameter to the + first module. Commas can be provided in module parameters by doubling + them on the command line to escape them: + +``-initrd "bzImage earlyprintk=xen,,keep root=/dev/xvda1,initrd.img"`` + Multiboot only. Use bzImage as the first module with + "``earlyprintk=xen,keep root=/dev/xvda1``" as its command line, + and initrd.img as the second module. + ERST DEF("dtb", HAS_ARG, QEMU_OPTION_dtb, \ |