x86: kvmclock: Do not setup kvmclock vsyscall in the absence of that clock

This fixes boot lockups with "no-kvmclock", when the host is not
exposing this particular feature (QEMU: -cpu ...,-kvmclock) or when
the kvmclock initialization failed for whatever reason.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 5bedbdddf1f2..b730efad6fe9 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -160,8 +160,12 @@ int kvm_register_clock(char *txt)
 {
         int cpu = smp_processor_id();
         int low, high, ret;
-        struct pvclock_vcpu_time_info *src = &hv_clock[cpu].pvti;
+        struct pvclock_vcpu_time_info *src;
+
+        if (!hv_clock)
+                return 0;
 
+        src = &hv_clock[cpu].pvti;
         low = (int)__pa(src) | 1;
         high = ((u64)__pa(src) >> 32);
         ret = native_write_msr_safe(msr_kvm_system_time, low, high);
@@ -276,6 +280,9 @@ int __init kvm_setup_vsyscall_timeinfo(void)
         struct pvclock_vcpu_time_info *vcpu_time;
         unsigned int size;
 
+        if (!hv_clock)
+                return 0;
+
         size = PAGE_ALIGN(sizeof(struct pvclock_vsyscall_time_info)*NR_CPUS);
 
         preempt_disable();