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Commit 1e977aa1 authored by Glauber Costa's avatar Glauber Costa Committed by Avi Kivity
Browse files

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: default avatarGlauber Costa <gcosta@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 3c62c625

arch/x86/kernel/kvmclock.c

+27 −0
Original line number Diff line number Diff line
@@ -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);

	}

}