KVM: KVM Steal time guest/host interface

To implement steal time, we need the hypervisor to pass the guest information
about how much time was spent running other processes outside the VM.
This is per-vcpu, and using the kvmclock structure for that is an abuse
we decided not to make.

In this patchset, I am introducing a new msr, KVM_MSR_STEAL_TIME, that
holds the memory area address containing information about steal time

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

Signed-off-by: Glauber Costa <glommer@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Tested-by: Eric B Munson <emunson@mgebm.net>
CC: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/Documentation/virtual/kvm/msr.txt b/Documentation/virtual/kvm/msr.txt
index d079aed27e03..50317809113d 100644
--- a/Documentation/virtual/kvm/msr.txt
+++ b/Documentation/virtual/kvm/msr.txt
@@ -185,3 +185,37 @@ MSR_KVM_ASYNC_PF_EN: 0x4b564d02
 
         Currently type 2 APF will be always delivered on the same vcpu as
         type 1 was, but guest should not rely on that.
+
+MSR_KVM_STEAL_TIME: 0x4b564d03
+
+        data: 64-byte alignment physical address of a memory area which must be
+        in guest RAM, plus an enable bit in bit 0. This memory is expected to
+        hold a copy of the following structure:
+
+        struct kvm_steal_time {
+                __u64 steal;
+                __u32 version;
+                __u32 flags;
+                __u32 pad[12];
+        }
+
+        whose data will be filled in by the hypervisor periodically. Only one
+        write, or registration, is needed for each VCPU. The interval between
+        updates of this structure is arbitrary and implementation-dependent.
+        The hypervisor may update this structure at any time it sees fit until
+        anything with bit0 == 0 is written to it. Guest is required to make sure
+        this structure is initialized to zero.
+
+        Fields have the following meanings:
+
+                version: a sequence counter. In other words, guest has to check
+                this field before and after grabbing time information and make
+                sure they are both equal and even. An odd version indicates an
+                in-progress update.
+
+                flags: At this point, always zero. May be used to indicate
+                changes in this structure in the future.
+
+                steal: the amount of time in which this vCPU did not run, in
+                nanoseconds. Time during which the vcpu is idle, will not be
+                reported as steal time.