From 4aa743788cd217a680d8f0ea2cb040088967be3e Mon Sep 17 00:00:00 2001
From: Glauber Costa <glommer@redhat.com>
Date: Wed, 23 Jun 2010 13:33:29 -0300
Subject: [PATCH 1/3] turn off kvmclock when resetting cpu

RH-Author: Glauber Costa <glommer@redhat.com>
Message-id: <1277300009-24438-1-git-send-email-glommer@redhat.com>
Patchwork-id: 10113
O-Subject: [RHEL5 PATCH] turn off kvmclock when resetting cpu
Bugzilla: 588878
RH-Acked-by: Avi Kivity <avi@redhat.com>
RH-Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
RH-Acked-by: Zachary Amsden <zamsden@redhat.com>

Ackers, you already did it for RHEL6, please re-ack for 5.
RH-Bugzilla: 588878
RH-Upstream-status: qemu-kvm/master
RH-Author: Glauber Costa <glommer@gmail.com>

Difference from upstream:

To avoid risking regressions in the RHEL5 timeframe, we skip loading the
TSC.

Upstream changelog:

Currently, in the linux kernel, we reset kvmclock if we are rebooting
into a crash kernel through kexec. The rationale, is that a new kernel
won't follow the same memory addresses, and the memory where kvmclock is
located in the first kernel, will be something else in the second one.

We don't do it in normal reboots, because the second kernel ends up
registering kvmclock again, which has the effect of turning off the
first instance.

This is, however, totally wrong. This assumes we're booting into
a kernel that also has kvmclock enabled. If by some reason we reboot
into something that doesn't do kvmclock including but not limited to:
 * rebooting into an older kernel without kvmclock support,
 * rebooting with no-kvmclock,
 * rebootint into another O.S,

we'll simply have the hypervisor writting into a random memory position
into the guest. Neat, uh?

Moreover, I believe the fix belongs in qemu, since it is the entity
more prepared to detect all kinds of reboots (by means of a cpu_reset),
not to mention the presence of misbehaving guests, that can forget
to turn kvmclock off.

It is also necessary to reset other msrs, so this patch resets
everything that kvm exports through its MSR list.

This patch fixes the issue for me.

Signed-off-by: Glauber Costa <glommer@redhat.com>
---
 qemu-kvm-x86.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 qemu/qemu-kvm-x86.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/qemu/qemu-kvm-x86.c b/qemu/qemu-kvm-x86.c
index 899f0ad..97c106d 100644
--- a/qemu/qemu-kvm-x86.c
+++ b/qemu/qemu-kvm-x86.c
@@ -767,8 +767,36 @@ int handle_tpr_access(void *opaque, int vcpu,
     return 0;
 }
 
+static void kvm_reset_msrs(CPUState *env)
+{
+    struct {
+        struct kvm_msrs info;
+        struct kvm_msr_entry entries[100];
+    } msr_data;
+    int n, n_msrs;
+    int rc;
+    struct kvm_msr_entry *msrs = msr_data.entries;
+
+    if (!kvm_msr_list)
+        return;
+
+    n_msrs = 0;
+    for (n = 0; n < kvm_msr_list->nmsrs; n++) {
+        if (kvm_msr_list->indices[n] == MSR_IA32_TSC)
+            continue;
+        set_msr_entry(&msrs[n_msrs++], kvm_msr_list->indices[n], 0);
+    }
+
+    msr_data.info.nmsrs = n_msrs;
+
+    rc = kvm_set_msrs(kvm_context, env->cpu_index, msrs, n_msrs);
+    if (rc == -1)
+        perror("kvm_set_msrs FAILED");
+}
+
 void kvm_arch_cpu_reset(CPUState *env)
 {
+    kvm_reset_msrs(env);
     env->nmi_injected = 0;
     env->nmi_pending = 0;
     kvm_load_vcpu_events(env);
-- 
1.7.0.3