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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>
This commit is contained in:
Glauber Costa 2008-03-17 16:08:40 -03:00 committed by Avi Kivity
parent 3c62c62502
commit 1e977aa12d
1 changed files with 27 additions and 0 deletions
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27
arch/x86/kernel/kvmclock.c
View File

@ -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);
}
}