There is a deadlock in pvclock handling:
cpu0: cpu1:
kvm_gen_update_masterclock()
kvm_guest_time_update()
spin_lock(pvclock_gtod_sync_lock)
local_irq_save(flags)
spin_lock(pvclock_gtod_sync_lock)
kvm_make_mclock_inprogress_request(kvm)
make_all_cpus_request()
smp_call_function_many()
Now if smp_call_function_many() called by cpu0 tries to call function on
cpu1 there will be a deadlock.
Fix by moving pvclock_gtod_sync_lock protected section outside irq
disabled section.
Analyzed by Gleb Natapov <gleb@xxxxxxxxxx>
Reported-and-Tested-by: Yongjie Ren <yongjie.ren@xxxxxxxxx>
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f71500a..f7c850b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1416,15 +1416,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
kernel_ns = 0;
host_tsc = 0;
- /* Keep irq disabled to prevent changes to the clock */
- local_irq_save(flags);
- this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
- if (unlikely(this_tsc_khz == 0)) {
- local_irq_restore(flags);
- kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
- return 1;
- }
-
/*
* If the host uses TSC clock, then passthrough TSC as stable
* to the guest.
@@ -1436,6 +1427,15 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
kernel_ns = ka->master_kernel_ns;
}
spin_unlock(&ka->pvclock_gtod_sync_lock);
+
+ /* Keep irq disabled to prevent changes to the clock */
+ local_irq_save(flags);
+ this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
+ if (unlikely(this_tsc_khz == 0)) {
+ local_irq_restore(flags);
+ kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
+ return 1;
+ }
if (!use_master_clock) {
host_tsc = native_read_tsc();
kernel_ns = get_kernel_ns();
--
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