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authorGlauber Costa <gcosta@redhat.com>2008-03-17 16:08:40 -0300
committerAvi Kivity <avi@qumranet.com>2008-04-27 12:00:31 +0300
commit1e977aa12dd4f80688b1f243762212e75c6d7fe8 (patch)
tree572941849e9d63c0de7233d2352d346dc097be49 /arch/x86/kernel
parent3c62c62502bea24448d4e82aa1f33c7dbca61a32 (diff)
x86: KVM guest: disable clock before rebooting.
This patch writes 0 (actually, what really matters is that the LSB is cleared) to the system time msr before shutting down the machine for kexec. Without it, we can have a random memory location being written when the guest comes back It overrides the functions shutdown, used in the path of kernel_kexec() (sys.c) and crash_shutdown, used in the path of crash_kexec() (kexec.c) Signed-off-by: Glauber Costa <gcosta@redhat.com> Signed-off-by: Avi Kivity <avi@qumranet.com>
Diffstat (limited to 'arch/x86/kernel')
-rw-r--r--arch/x86/kernel/kvmclock.c27
1 files changed, 27 insertions, 0 deletions
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index b999f5e5b3b..ddee04043ae 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -22,6 +22,7 @@
#include <asm/msr.h>
#include <asm/apic.h>
#include <linux/percpu.h>
+#include <asm/reboot.h>
#define KVM_SCALE 22
@@ -143,6 +144,28 @@ static void kvm_setup_secondary_clock(void)
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, this memory
+ * won't be valid. In cases like kexec, in which you install a new kernel, this
+ * means 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
+ */
+#ifdef CONFIG_KEXEC
+static void kvm_crash_shutdown(struct pt_regs *regs)
+{
+ native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0);
+ native_machine_crash_shutdown(regs);
+}
+#endif
+
+static void kvm_shutdown(void)
+{
+ native_write_msr_safe(MSR_KVM_SYSTEM_TIME, 0, 0);
+ native_machine_shutdown();
+}
+
void __init kvmclock_init(void)
{
if (!kvm_para_available())
@@ -155,6 +178,10 @@ 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.shutdown = kvm_shutdown;
+#ifdef CONFIG_KEXEC
+ machine_ops.crash_shutdown = kvm_crash_shutdown;
+#endif
clocksource_register(&kvm_clock);
}
}