[PATCH] disable clock before rebooting.

Glauber Costa
2008-03-06T16:14:52Z

This patch writes 0 (actually, what really matters is that the
LSB is cleared) to the system time msr before rebooting/shutting down
the machine.

Without it, we can have a random memory location being written
when the guest comes back

Signed-off-by: Glauber Costa <gcosta@redhat.com>
---
arch/x86/kernel/kvmclock.c | 32 ++++++++++++++++++++++++++++++++
1 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index f654a12..5c9ff8d 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -21,6 +21,7 @@ #include <linux/kvm_para.h>
#include <asm/arch_hooks.h>
#include <asm/msr.h>
#include <linux/percpu.h>
+#include <asm/reboot.h>

#define KVM_SCALE 22

@@ -142,6 +143,32 @@ static void kvm_setup_secondary_clock(vo
setup_secondary_APIC_clock();
}

+/*
+ * After the clock is registered, the host will keep writing to the
+ * registered memory location. If the guest happens to shutdown, or restart,
+ * this memory won't be valid. In cases like kexec, in which you install a new kernel,
+ * this will mean a random memory location will be kept being written. So before
+ * any kind of shutdown from our side, we unregister the clock by writting anything
+ * that does not have the 'enable' bit set in the msr
+ */
+static void kvm_restart(char *unused) {
+ native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0);
+ native_machine_restart(unused);
+}
+
+/* Forgive me dear lord, for my laziness */
+#define kvm_reboot_fn(x) \
+static void kvm_##x(void) { \
+ native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0); \
+ native_machine_##x(); \
+}
+
+kvm_reboot_fn(emergency_restart)
+kvm_reboot_fn(shutdown)
+kvm_reboot_fn(halt)
+kvm_reboot_fn(power_off)
+#undef kvm_reboot_fn
+
void __init kvmclock_init(void)
{
if (!kvm_para_available())
@@ -154,6 +181,11 @@ void __init kvmclock_init(void)
pv_time_ops.set_wallclock = kvm_set_wallclock;
pv_time_ops.sched_clock = kvm_clock_read;
pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock;
+ machine_ops.emergency_restart = kvm_emergency_restart;
+ machine_ops.shutdown = kvm_shutdown;
+ machine_ops.restart = kvm_restart;
+ machine_ops.halt = kvm_halt;
+ machine_ops.power_off = kvm_power_off;
clocksource_register(&kvm_clock);
}
}
--
1.4.2