On 29.06.2011, at 13:53, Josh Boyer wrote:

On Wed, Jun 29, 2011 at 08:41:03PM +1000, Paul Mackerras wrote:

quoted

Documentation/virtual/kvm/api.txt   |   35 =

+++++++++++++++++++++++++++++++++++

quoted

arch/powerpc/include/asm/kvm.h      |   15 +++++++++++++++
arch/powerpc/include/asm/kvm_host.h |    1 +
arch/powerpc/kvm/powerpc.c          |   28 =

++++++++++++++++++++++++++++

quoted

include/linux/kvm.h                 |    1 +
5 files changed, 80 insertions(+), 0 deletions(-)
=20

diff --git a/Documentation/virtual/kvm/api.txt =

b/Documentation/virtual/kvm/api.txt

quoted

index b0e4b9c..3ab012c 100644

--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt

@@ -1430,6 +1430,41 @@ is supported; 2 if the processor requires all =

virtual machines to have

quoted

an RMA, or 1 if the processor can use an RMA but doesn't require it,
because it supports the Virtual RMA (VRMA) facility.
=20
+4.64 KVM_PPC_SET_PLATFORM
+
+Capability: none
+Architectures: powerpc
+Type: vm ioctl
+Parameters: struct kvm_ppc_set_platform (in)
+Returns: 0, or -1 on error
+
+This is used by userspace to tell KVM what sort of platform it =

should

quoted

+emulate.  The return value of the ioctl tells userspace whether the
+emulation it is requesting is supported by KVM.
+
+struct kvm_ppc_set_platform {
+	__u16 platform;		/* defines the OS/hypervisor ABI */
+	__u16 guest_arch;	/* e.g. decimal 206 for v2.06 */
+	__u32 flags;
+};
+
+/* Values for platform */
+#define KVM_PPC_PV_NONE		0	/* bare-metal, =

non-paravirtualized */

quoted

+#define KVM_PPC_PV_KVM		1	/* as defined in =

kvm_para.h */

quoted

+#define KVM_PPC_PV_SPAPR	2	/* IBM Server PAPR (a la =

PowerVM) */

quoted

+
+/* Values for flags */
+#define KVM_PPC_CROSS_ARCH	1	/* guest architecture !=3D host =

*/

quoted

+
+The KVM_PPC_CROSS_ARCH bit being 1 indicates that the guest is of a
+sufficiently different architecture to the host that the guest =

cannot

quoted

+be permitted to use supervisor mode.  For example, if the host is a
+64-bit machine and the guest is a 32-bit machine, then this bit =

should

quoted

+be set.

=20
This makes me wonder if a similar thing might eventually be usable for
running an i686 or x32 guest on an x86_64 KVM host.  I have no idea if
that is even theoretically possible, but if it is it might be better =

to

rename the ioctl to be architecture agnostic.

On x86 this is not required unless we want to "virtualize" pre-CPUID =
CPUs. Everything as of Pentium has a full bitmap of feature capabilities =
that KVM gets from user space, including information such as "Can we do =
64-bit mode?".


Alex