KVM: add MSR based hypercall API

This adds a special MSR based hypercall API to KVM. This is to be
used by paravirtual kernels and virtual drivers.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/include/linux/kvm_para.h b/include/linux/kvm_para.h
new file mode 100644
index 000000000000..74be5c1002ec
--- /dev/null
+++ b/include/linux/kvm_para.h
@@ -0,0 +1,55 @@
+#ifndef __LINUX_KVM_PARA_H
+#define __LINUX_KVM_PARA_H
+
+/*
+ * Guest OS interface for KVM paravirtualization
+ *
+ * Note: this interface is totally experimental, and is certain to change
+ *       as we make progress.
+ */
+
+/*
+ * Per-VCPU descriptor area shared between guest and host. Writable to
+ * both guest and host. Registered with the host by the guest when
+ * a guest acknowledges paravirtual mode.
+ *
+ * NOTE: all addresses are guest-physical addresses (gpa), to make it
+ * easier for the hypervisor to map between the various addresses.
+ */
+struct kvm_vcpu_para_state {
+        /*
+         * API version information for compatibility. If there's any support
+         * mismatch (too old host trying to execute too new guest) then
+         * the host will deny entry into paravirtual mode. Any other
+         * combination (new host + old guest and new host + new guest)
+         * is supposed to work - new host versions will support all old
+         * guest API versions.
+         */
+        u32 guest_version;
+        u32 host_version;
+        u32 size;
+        u32 ret;
+
+        /*
+         * The address of the vm exit instruction (VMCALL or VMMCALL),
+         * which the host will patch according to the CPU model the
+         * VM runs on:
+         */
+        u64 hypercall_gpa;
+
+} __attribute__ ((aligned(PAGE_SIZE)));
+
+#define KVM_PARA_API_VERSION 1
+
+/*
+ * This is used for an RDMSR's ECX parameter to probe for a KVM host.
+ * Hopefully no CPU vendor will use up this number. This is placed well
+ * out of way of the typical space occupied by CPU vendors' MSR indices,
+ * and we think (or at least hope) it wont be occupied in the future
+ * either.
+ */
+#define MSR_KVM_API_MAGIC 0x87655678
+
+#define KVM_EINVAL 1
+
+#endif