[PATCH 1/3] KVM paravirt_ops infrastructure

Anthony Liguori
2007-05-30T14:52:23Z

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Regards,

Anthony Liguori

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Subject: [PATCH] Add KVM paravirt_ops implementation
From: Anthony Liguori <aliguori@us.ibm.com>

This patch adds the basic infrastructure for paravirtualizing a KVM guest.
Discovery of running under KVM is done by sharing a page of memory between
the guest and host (initially through an MSR write).

This is based on a patch written by Ingo Molnar.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Index: kvm/arch/i386/Kconfig
===================================================================
--- kvm.orig/arch/i386/Kconfig 2007-05-30 08:42:31.000000000 -0500
+++ kvm/arch/i386/Kconfig 2007-05-30 08:42:38.000000000 -0500
@@ -231,6 +231,13 @@
at the moment), by linking the kernel to a GPL-ed ROM module
provided by the hypervisor.

+config KVM_GUEST
+ bool "KVM paravirt-ops support"
+ depends on PARAVIRT
+ help
+ This option enables various optimizations for running under the KVM
+ hypervisor.
+
config ACPI_SRAT
bool
default y
Index: kvm/arch/i386/kernel/Makefile
===================================================================
--- kvm.orig/arch/i386/kernel/Makefile 2007-05-30 08:42:26.000000000 -0500
+++ kvm/arch/i386/kernel/Makefile 2007-05-30 08:42:38.000000000 -0500
@@ -41,6 +41,7 @@
obj-$(CONFIG_K8_NB) += k8.o

obj-$(CONFIG_VMI) += vmi.o vmiclock.o
+obj-$(CONFIG_KVM_GUEST) += kvm.o
obj-$(CONFIG_PARAVIRT) += paravirt.o
obj-y += pcspeaker.o

Index: kvm/arch/i386/kernel/kvm.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ kvm/arch/i386/kernel/kvm.c 2007-05-30 09:29:37.000000000 -0500
@@ -0,0 +1,100 @@
+/*
+ * KVM paravirt_ops implementation
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * Copyright (C) 2007, Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ * Copyright IBM Corporation, 2007
+ * Authors: Anthony Liguori <aliguori@us.ibm.com>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/kvm_para.h>
+#include <linux/cpu.h>
+
+static DEFINE_PER_CPU(struct kvm_vcpu_para_state, para_state);
+extern unsigned char hypercall_addr[4];
+
+static void kvm_guest_setup(void)
+{
+ paravirt_ops.name = "KVM";
+ paravirt_ops.paravirt_enabled = 1;
+}
+
+/*
+ * This is the vm-syscall address - to be patched by the host to
+ * VMCALL (Intel) or VMMCALL (AMD), depending on the CPU model:
+ */
+asm (
+ ".globl hypercall_addr\n"
+ ".align 4\n"
+ "hypercall_addr:\n"
+ "movl $-38, %eax\n"
+ "ret\n"
+);
+
+static int kvm_guest_register_para(int cpu)
+{
+ struct kvm_vcpu_para_state *para_state = &per_cpu(para_state, cpu);
+
+ printk(KERN_DEBUG "kvm guest on VCPU#%d: trying to register para_state %p\n",
+ cpu, para_state);
+
+ /*
+ * Try to write to a magic MSR (which is invalid on any real CPU),
+ * and thus signal to KVM that we wish to entering paravirtualized
+ * mode:
+ */
+ para_state->guest_version = KVM_PARA_API_VERSION;
+ para_state->host_version = -1;
+ para_state->size = sizeof(*para_state);
+ para_state->ret = 0;
+ para_state->hypercall_gpa = __pa(hypercall_addr);
+
+ if (wrmsr_safe(MSR_KVM_API_MAGIC, __pa(para_state), 0)) {
+ printk(KERN_INFO "KVM guest: WRMSR probe failed.\n");
+ return -ENOENT;
+ }
+
+ printk(KERN_DEBUG "kvm guest: host returned %d\n", para_state->ret);
+ printk(KERN_DEBUG "kvm guest: host version: %d\n", para_state->host_version);
+ printk(KERN_DEBUG "kvm guest: syscall entry: %02x %02x %02x %02x\n",
+ hypercall_addr[0], hypercall_addr[1],
+ hypercall_addr[2], hypercall_addr[3]);
+
+ if (para_state->ret) {
+ printk(KERN_ERR "kvm guest: host refused registration.\n");
+ return para_state->ret;
+ }
+
+ return 0;
+}
+
+static int __init kvm_guest_init(void)
+{
+ int rc;
+
+ rc = kvm_guest_register_para(smp_processor_id());
+ if (rc) {
+ printk(KERN_INFO "paravirt KVM unavailable\n");
+ goto out;
+ }
+
+ kvm_guest_setup();
+ out:
+ return 0;
+}
+core_initcall(kvm_guest_init);

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