Merge branch 'xenfv-kvm-15' of git://git.infradead.org/users/dwmw2/qemu into HEAD

This adds support for emulating Xen under Linux/KVM, based on kernel
patches which have been present since Linux v5.12. As with the kernel
support, it's derived from work started by João Martins of Oracle in
2018.

This series just adds the basic platform support — CPUID, hypercalls,
event channels, a stub of XenStore.

A full single-tenant internal implementation of XenStore, and patches
to make QEMU's Xen PV drivers work with this Xen emulation, are waiting
in the wings to be submitted in a follow-on patch series.

As noted in the documentation, it's enabled by setting the xen-version
property on the KVM accelerator, e.g.:

 qemu-system-x86_64 -serial mon:stdio -M q35 -display none -m 1G -smp 2 \
    -accel kvm,xen-version=0x4000e,kernel-irqchip=split \
    -kernel vmlinuz-6.0.7-301.fc37.x86_64 \
    -append "console=ttyS0 root=/dev/sda1" \
    -drive file=/var/lib/libvirt/images/fedora28.qcow2,if=none,id=disk \
    -device ahci,id=ahci -device ide-hd,drive=disk,bus=ahci.0

Even before this was merged, we've already been using it to find and fix
bugs in the Linux kernel Xen guest support:

https://lore.kernel.org/all/4bffa69a949bfdc92c4a18e5a1c3cbb3b94a0d32.camel@infradead.org/
https://lore.kernel.org/all/871qnunycr.ffs@tglx/

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 16 insertions, 5 deletions

diff --git a/include/hw/xen/xen.h b/include/hw/xen/xen.h
index afdf9c436a..03983939f9 100644
--- a/include/hw/xen/xen.h
+++ b/include/hw/xen/xen.h
@@ -1,19 +1,30 @@
-#ifndef QEMU_HW_XEN_H
-#define QEMU_HW_XEN_H
-
 /*
  * public xen header
  *   stuff needed outside xen-*.c, i.e. interfaces to qemu.
  *   must not depend on any xen headers being present in
  *   /usr/include/xen, so it can be included unconditionally.
  */
+#ifndef QEMU_HW_XEN_H
+#define QEMU_HW_XEN_H
+
+/*
+ * As a temporary measure while the headers are being untangled, define
+ * __XEN_TOOLS__ here before any Xen headers are included. Otherwise, if
+ * the Xen toolstack library headers are later included, they will find
+ * some of the "internal" definitions missing and the build will fail. In
+ * later commits, we'll end up with a rule that the native libraries have
+ * to be included first, which will ensure that the libraries get the
+ * version of Xen libraries that they expect.
+ */
+#define __XEN_TOOLS__ 1
 
 #include "exec/cpu-common.h"
 
 /* xen-machine.c */
 enum xen_mode {
-    XEN_EMULATE = 0,  // xen emulation, using xenner (default)
-    XEN_ATTACH        // attach to xen domain created by libxl
+    XEN_DISABLED = 0, /* xen support disabled (default) */
+    XEN_ATTACH,       /* attach to xen domain created by libxl */
+    XEN_EMULATE,      /* emulate Xen within QEMU */
 };
 
 extern uint32_t xen_domid;