KVM: Xen PV-on-HVM guest support

Support for Xen PV-on-HVM guests can be implemented almost entirely in
userspace, except for handling one annoying MSR that maps a Xen
hypercall blob into guest address space.

A generic mechanism to delegate MSR writes to userspace seems overkill
and risks encouraging similar MSR abuse in the future.  Thus this patch
adds special support for the Xen HVM MSR.

I implemented a new ioctl, KVM_XEN_HVM_CONFIG, that lets userspace tell
KVM which MSR the guest will write to, as well as the starting address
and size of the hypercall blobs (one each for 32-bit and 64-bit) that
userspace has loaded from files.  When the guest writes to the MSR, KVM
copies one page of the blob from userspace to the guest.

I've tested this patch with a hacked-up version of Gerd's userspace
code, booting a number of guests (CentOS 5.3 i386 and x86_64, and
FreeBSD 8.0-RC1 amd64) and exercising PV network and block devices.

[jan: fix i386 build warning]
[avi: future proof abi with a flags field]

Signed-off-by: Ed Swierk <eswierk@aristanetworks.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

2 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
index f02e87a5206f..ef9b4b73cce4 100644
--- a/arch/x86/include/asm/kvm.h
+++ b/arch/x86/include/asm/kvm.h
@@ -19,6 +19,7 @@
 #define __KVM_HAVE_MSIX
 #define __KVM_HAVE_MCE
 #define __KVM_HAVE_PIT_STATE2
+#define __KVM_HAVE_XEN_HVM
 
 /* Architectural interrupt line count. */
 #define KVM_NR_INTERRUPTS 256
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 179a919f53a4..36f3b53f5c27 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -410,6 +410,8 @@ struct kvm_arch{
 
         unsigned long irq_sources_bitmap;
         u64 vm_init_tsc;
+
+        struct kvm_xen_hvm_config xen_hvm_config;
 };
 
 struct kvm_vm_stat {