Commit message: KVM guest: prevent tracing recursion with kvmclock

Prevent tracing of preempt_disable() in get_cpu_var() in
kvm_clock_read(). When CONFIG_DEBUG_PREEMPT is enabled,
preempt_disable/enable() are traced and this causes the function_graph
tracer to go into an infinite recursion. By open coding the
preempt_disable() around the get_cpu_var(), we can use the notrace
version which prevents preempt_disable/enable() from being traced and
prevents the recursion.

Based on a similar patch for Xen from Jeremy Fitzhardinge.

Tested-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Avi Kivity <avi@redhat.com>
CVE: None
Vulnerability description: None

Project: linux
File: kvmclock.c

static int parse_no_kvmclock(char *arg)
{
	kvmclock = 0;
	return 0;
}

Project: linux
File: kvmclock.c

static void __cpuinit kvm_setup_secondary_clock(void)
{
	/*
	 * Now that the first cpu already had this clocksource initialized,
	 * we shouldn't fail.
	 */
	WARN_ON(kvm_register_clock("secondary cpu clock"));
	/* ok, done with our trickery, call native */
	setup_secondary_APIC_clock();
}

Project: linux
File: kvmclock.c

static int kvm_set_wallclock(unsigned long now)
{
	return -1;
}

Project: linux
File: kvmclock.c

static void kvm_get_preset_lpj(void)
{
	unsigned long khz;
	u64 lpj;

	khz = kvm_get_tsc_khz();

	lpj = ((u64)khz * 1000);
	do_div(lpj, HZ);
	preset_lpj = lpj;
}

Project: linux
File: kvmclock.c

static unsigned long kvm_get_wallclock(void)
{
	struct pvclock_vcpu_time_info *vcpu_time;
	struct timespec ts;
	int low, high;

	low = (int)__pa_symbol(&wall_clock);
	high = ((u64)__pa_symbol(&wall_clock) >> 32);

	native_write_msr(msr_kvm_wall_clock, low, high);

	vcpu_time = &get_cpu_var(hv_clock);
	pvclock_read_wallclock(&wall_clock, vcpu_time, &ts);
	put_cpu_var(hv_clock);

	return ts.tv_sec;
}

Project: linux
File: kvmclock.c

static cycle_t kvm_clock_get_cycles(struct clocksource *cs)
{
	return kvm_clock_read();
}

Project: linux
File: kvmclock.c

static unsigned long kvm_get_tsc_khz(void)
{
	struct pvclock_vcpu_time_info *src;
	src = &per_cpu(hv_clock, 0);
	return pvclock_tsc_khz(src);
}

Project: linux
File: kvmclock.c

static void kvm_shutdown(void)
{
	native_write_msr(msr_kvm_system_time, 0, 0);
	kvm_disable_steal_time();
	native_machine_shutdown();
}

Project: linux
File: kvmclock.c

static cycle_t kvm_clock_read(void)
{
	struct pvclock_vcpu_time_info *src;
	cycle_t ret;

	preempt_disable_notrace();
	src = &__get_cpu_var(hv_clock);
	ret = pvclock_clocksource_read(src);
	preempt_enable_notrace();
	return ret;
}

Project: linux
File: kvmclock.c

void __init kvmclock_init(void)
{
	if (!kvm_para_available())
		return;

	if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
		msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
		msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
	} else if (!(kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)))
		return;

	printk(KERN_INFO "kvm-clock: Using msrs %x and %x",
		msr_kvm_system_time, msr_kvm_wall_clock);

	if (kvm_register_clock("boot clock"))
		return;
	pv_time_ops.sched_clock = kvm_clock_read;
	x86_platform.calibrate_tsc = kvm_get_tsc_khz;
	x86_platform.get_wallclock = kvm_get_wallclock;
	x86_platform.set_wallclock = kvm_set_wallclock;
#ifdef CONFIG_X86_LOCAL_APIC
	x86_cpuinit.setup_percpu_clockev =
		kvm_setup_secondary_clock;
#endif
	machine_ops.shutdown  = kvm_shutdown;
#ifdef CONFIG_KEXEC
	machine_ops.crash_shutdown  = kvm_crash_shutdown;
#endif
	kvm_get_preset_lpj();
	clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
	pv_info.paravirt_enabled = 1;
	pv_info.name = "KVM";

	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
		pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
}

Project: linux
File: kvmclock.c

static void kvm_crash_shutdown(struct pt_regs *regs)
{
	native_write_msr(msr_kvm_system_time, 0, 0);
	kvm_disable_steal_time();
	native_machine_crash_shutdown(regs);
}

Project: linux
File: kvmclock.c

int kvm_register_clock(char *txt)
{
	int cpu = smp_processor_id();
	int low, high, ret;

	low = (int)__pa(&per_cpu(hv_clock, cpu)) | 1;
	high = ((u64)__pa(&per_cpu(hv_clock, cpu)) >> 32);
	ret = native_write_msr_safe(msr_kvm_system_time, low, high);
	printk(KERN_INFO "kvm-clock: cpu %d, msr %x:%x, %s\n",
	       cpu, high, low, txt);

	return ret;
}