Re: [PATCH 03/16] KVM-HDR: KVM Userspace registering ioctl

From: Avi Kivity
Date: Wed Jan 26 2011 - 06:12:14 EST

On 01/24/2011 08:06 PM, Glauber Costa wrote:
KVM, which stands for KVM Virtual Memory (I wanted to call it KVM Virtual Mojito),
is a piece of shared memory that is visible to both the hypervisor and the guest
kernel - but not the guest userspace.

The basic idea is that the guest can tell the hypervisor about a specific
piece of memory, and what it expects to find in there. This is a generic
abstraction, that goes to userspace (qemu) if KVM (the hypervisor) can't
handle a specific request, thus giving us flexibility in some features
in the future.

KVM (The hypervisor) can change the contents of this piece of memory at
will. This works well with paravirtual information, and hopefully
normal guest memory - like last update time for the watchdog, for

This patch contains the header part of the userspace communication implementation.
Userspace can query the presence/absence of this feature in the normal way.
It also tells the hypervisor that it is capable of handling - in whatever
way it chooses, registrations that the hypervisor does not know how to.
In x86, only user so far, this mechanism is implemented as generic userspace
msr exit, that could theorectically be used to implement msr-handling in

I am keeping the headers separate to facilitate backports to people
who wants to backport the kernel part but not the hypervisor, or the other way around.

Again the protocol is not specified. How about starting from Documentation/kvm/api.txt so we don't have to guess?

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index ea2dc1a..5cc4fe8 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -161,6 +161,7 @@ struct kvm_pit_config {
#define KVM_EXIT_NMI 16
#define KVM_EXIT_OSI 18
+#define KVM_EXIT_X86_MSR_OP 19

@@ -541,6 +551,7 @@ struct kvm_ppc_pvinfo {
#define KVM_CAP_ASYNC_PF 59

These two seem completely unrelated.

error compiling committee.c: too many arguments to function

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