提交 3f804f6d 编写于 作者: T Thomas Gleixner 提交者: Paolo Bonzini

KVM: x86: Prevent deadlock against tk_core.seq

syzbot reported a possible deadlock in pvclock_gtod_notify():

CPU 0  		  	   	    	    CPU 1
write_seqcount_begin(&tk_core.seq);
  pvclock_gtod_notify()			    spin_lock(&pool->lock);
    queue_work(..., &pvclock_gtod_work)	    ktime_get()
     spin_lock(&pool->lock);		      do {
     						seq = read_seqcount_begin(tk_core.seq)
						...
				              } while (read_seqcount_retry(&tk_core.seq, seq);

While this is unlikely to happen, it's possible.

Delegate queue_work() to irq_work() which postpones it until the
tk_core.seq write held region is left and interrupts are reenabled.

Fixes: 16e8d74d ("KVM: x86: notifier for clocksource changes")
Reported-by: syzbot+6beae4000559d41d80f8@syzkaller.appspotmail.com
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Message-Id: <87h7jgm1zy.ffs@nanos.tec.linutronix.de>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
上级 594b27e6
......@@ -8094,6 +8094,18 @@ static void pvclock_gtod_update_fn(struct work_struct *work)
static DECLARE_WORK(pvclock_gtod_work, pvclock_gtod_update_fn);
/*
* Indirection to move queue_work() out of the tk_core.seq write held
* region to prevent possible deadlocks against time accessors which
* are invoked with work related locks held.
*/
static void pvclock_irq_work_fn(struct irq_work *w)
{
queue_work(system_long_wq, &pvclock_gtod_work);
}
static DEFINE_IRQ_WORK(pvclock_irq_work, pvclock_irq_work_fn);
/*
* Notification about pvclock gtod data update.
*/
......@@ -8105,13 +8117,14 @@ static int pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused,
update_pvclock_gtod(tk);
/* disable master clock if host does not trust, or does not
* use, TSC based clocksource.
/*
* Disable master clock if host does not trust, or does not use,
* TSC based clocksource. Delegate queue_work() to irq_work as
* this is invoked with tk_core.seq write held.
*/
if (!gtod_is_based_on_tsc(gtod->clock.vclock_mode) &&
atomic_read(&kvm_guest_has_master_clock) != 0)
queue_work(system_long_wq, &pvclock_gtod_work);
irq_work_queue(&pvclock_irq_work);
return 0;
}
......@@ -8224,6 +8237,7 @@ void kvm_arch_exit(void)
cpuhp_remove_state_nocalls(CPUHP_AP_X86_KVM_CLK_ONLINE);
#ifdef CONFIG_X86_64
pvclock_gtod_unregister_notifier(&pvclock_gtod_notifier);
irq_work_sync(&pvclock_irq_work);
cancel_work_sync(&pvclock_gtod_work);
#endif
kvm_x86_ops.hardware_enable = NULL;
......
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