Merge tag 'xenfv-2' of git://git.infradead.org/users/dwmw2/qemu into staging

Enable PV backends with Xen/KVM emulation

This is phase 2, following on from the basic platform support which was
already merged.

 • Add a simple single-tenant internal XenStore implementation
 • Indirect Xen gnttab/evtchn/foreignmem/xenstore through operations table
 • Provide emulated back ends for Xen operations
 • Header cleanups to allow PV back ends to build without Xen itself
 • Enable PV back ends in emulated mode
 • Documentation update

Tested-by: Paul Durrant <paul@xen.org>
... on real Xen (master branch, 4.18) with a Debian guest.

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* tag 'xenfv-2' of git://git.infradead.org/users/dwmw2/qemu: (27 commits)
  docs: Update Xen-on-KVM documentation for PV disk support
  MAINTAINERS: Add entry for Xen on KVM emulation
  i386/xen: Initialize Xen backends from pc_basic_device_init() for emulation
  hw/xen: Implement soft reset for emulated gnttab
  hw/xen: Map guest XENSTORE_PFN grant in emulated Xenstore
  hw/xen: Add emulated implementation of XenStore operations
  hw/xen: Add emulated implementation of grant table operations
  hw/xen: Hook up emulated implementation for event channel operations
  hw/xen: Only advertise ring-page-order for xen-block if gnttab supports it
  hw/xen: Avoid crash when backend watch fires too early
  hw/xen: Build PV backend drivers for CONFIG_XEN_BUS
  hw/xen: Rename xen_common.h to xen_native.h
  hw/xen: Use XEN_PAGE_SIZE in PV backend drivers
  hw/xen: Move xenstore_store_pv_console_info to xen_console.c
  hw/xen: Add xenstore operations to allow redirection to internal emulation
  hw/xen: Add foreignmem operations to allow redirection to internal emulation
  hw/xen: Pass grant ref to gnttab unmap operation
  hw/xen: Add gnttab operations to allow redirection to internal emulation
  hw/xen: Add evtchn operations to allow redirection to internal emulation
  hw/xen: Create initial XenStore nodes
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 23 insertions, 7 deletions

diff --git a/docs/system/i386/xen.rst b/docs/system/i386/xen.rst
index a00523b492..f06765e88c 100644
--- a/docs/system/i386/xen.rst
+++ b/docs/system/i386/xen.rst
@@ -9,6 +9,8 @@ KVM has support for hosting Xen guests, intercepting Xen hypercalls and event
 channel (Xen PV interrupt) delivery. This allows guests which expect to be
 run under Xen to be hosted in QEMU under Linux/KVM instead.
 
+Using the split irqchip is mandatory for Xen support.
+
 Setup
 -----
 
@@ -17,14 +19,14 @@ accelerator, for example for Xen 4.10:
 
 .. parsed-literal::
 
-  |qemu_system| --accel kvm,xen-version=0x4000a
+  |qemu_system| --accel kvm,xen-version=0x4000a,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 --cpu host,+xen_vapic
+  |qemu_system| --accel kvm,xen-version=0x4000a,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
@@ -33,11 +35,25 @@ 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. Note that until the Xen PV device back ends are enabled to work
-with Xen mode in QEMU, that is unlikely to cause significant joy. Linux guests
-can be dissuaded from this by adding 'xen_emul_unplug=never' on their command
-line, and it can also be noted that AHCI disk controllers are exempt from being
-unplugged, as are passthrough VFIO PCI devices.
+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
 ----------