[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[PATCH v2 24/24] docs: update Xen-on-KVM documentation
From: |
David Woodhouse |
Subject: |
[PATCH v2 24/24] docs: update Xen-on-KVM documentation |
Date: |
Thu, 19 Oct 2023 16:40:20 +0100 |
From: David Woodhouse <dwmw@amazon.co.uk>
Add notes about console and network support, and how to launch PV guests.
Clean up the disk configuration examples now that that's simpler, and
remove the comment about IDE unplug on q35/AHCI now that it's fixed.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
docs/system/i386/xen.rst | 100 ++++++++++++++++++++++++++++-----------
1 file changed, 72 insertions(+), 28 deletions(-)
diff --git a/docs/system/i386/xen.rst b/docs/system/i386/xen.rst
index f06765e88c..6214c4571e 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 +64,71 @@ 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 -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 user``
+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.
+
+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
--
2.40.1
- [PATCH v2 11/24] hw/xen: automatically assign device index to block devices, (continued)
- [PATCH v2 11/24] hw/xen: automatically assign device index to block devices, David Woodhouse, 2023/10/19
- [PATCH v2 15/24] hw/xen: add support for Xen primary console in emulated mode, David Woodhouse, 2023/10/19
- [PATCH v2 03/24] hw/xen: select kernel mode for per-vCPU event channel upcall vector, David Woodhouse, 2023/10/19
- [PATCH v2 12/24] hw/xen: add get_frontend_path() method to XenDeviceClass, David Woodhouse, 2023/10/19
- [PATCH v2 07/24] hw/xen: Clean up event channel 'type_val' handling to use union, David Woodhouse, 2023/10/19
- [PATCH v2 04/24] hw/xen: don't clear map_track[] in xen_gnttab_reset(), David Woodhouse, 2023/10/19
- [PATCH v2 08/24] include: update Xen public headers to Xen 4.17.2 release, David Woodhouse, 2023/10/19
- [PATCH v2 13/24] hw/xen: do not repeatedly try to create a failing backend device, David Woodhouse, 2023/10/19
- [PATCH v2 09/24] i386/xen: advertise XEN_HVM_CPUID_UPCALL_VECTOR in CPUID, David Woodhouse, 2023/10/19
- [PATCH v2 02/24] i386/xen: fix per-vCPU upcall vector for Xen emulation, David Woodhouse, 2023/10/19
- [PATCH v2 24/24] docs: update Xen-on-KVM documentation,
David Woodhouse <=
- [PATCH v2 18/24] hw/xen: update Xen PV NIC to XenDevice model, David Woodhouse, 2023/10/19
- [PATCH v2 22/24] tests/avocado: switch to using xen-net-device for Xen guest tests, David Woodhouse, 2023/10/19
- [PATCH v2 17/24] hw/xen: only remove peers of PCI NICs on unplug, David Woodhouse, 2023/10/19
- [PATCH v2 06/24] i386/xen: Ignore VCPU_SSHOTTMR_future flag in set_singleshot_timer(), David Woodhouse, 2023/10/19
- [PATCH v2 14/24] hw/xen: update Xen console to XenDevice model, David Woodhouse, 2023/10/19
- [PATCH v2 23/24] xen-platform: unplug AHCI disks, David Woodhouse, 2023/10/19