Commit a83829f5 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: x86: disable interrupts while pvclock_gtod_sync_lock is taken 



pvclock_gtod_sync_lock can be taken with interrupts disabled if the
preempt notifier calls get_kvmclock_ns to update the Xen
runstate information:

   spin_lock include/linux/spinlock.h:354 [inline]
   get_kvmclock_ns+0x25/0x390 arch/x86/kvm/x86.c:2587
   kvm_xen_update_runstate+0x3d/0x2c0 arch/x86/kvm/xen.c:69
   kvm_xen_update_runstate_guest+0x74/0x320 arch/x86/kvm/xen.c:100
   kvm_xen_runstate_set_preempted arch/x86/kvm/xen.h:96 [inline]
   kvm_arch_vcpu_put+0x2d8/0x5a0 arch/x86/kvm/x86.c:4062

So change the users of the spinlock to spin_lock_irqsave and
spin_unlock_irqrestore.

Reported-by: default avatar <syzbot+b282b65c2c68492df769@syzkaller.appspotmail.com>
Fixes: 30b5c851 ("KVM: x86/xen: Add support for vCPU runstate information")
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c2c647f9

arch/x86/kvm/x86.c

+14 −11
Original line number Diff line number Diff line
@@ -2328,7 +2328,7 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data) 
	kvm_vcpu_write_tsc_offset(vcpu, offset);

	raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);



	spin_lock(&kvm->arch.pvclock_gtod_sync_lock);

	spin_lock_irqsave(&kvm->arch.pvclock_gtod_sync_lock, flags);

	if (!matched) {

		kvm->arch.nr_vcpus_matched_tsc = 0;

	} else if (!already_matched) {
@@ -2336,7 +2336,7 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data) 
	}



	kvm_track_tsc_matching(vcpu);

	spin_unlock(&kvm->arch.pvclock_gtod_sync_lock);

	spin_unlock_irqrestore(&kvm->arch.pvclock_gtod_sync_lock, flags);

}



static inline void adjust_tsc_offset_guest(struct kvm_vcpu *vcpu,
@@ -2558,15 +2558,16 @@ static void kvm_gen_update_masterclock(struct kvm *kvm) 
	int i;

	struct kvm_vcpu *vcpu;

	struct kvm_arch *ka = &kvm->arch;

	unsigned long flags;



	kvm_hv_invalidate_tsc_page(kvm);



	kvm_make_mclock_inprogress_request(kvm);



	/* no guest entries from this point */

	spin_lock(&ka->pvclock_gtod_sync_lock);

	spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags);

	pvclock_update_vm_gtod_copy(kvm);

	spin_unlock(&ka->pvclock_gtod_sync_lock);

	spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags);



	kvm_for_each_vcpu(i, vcpu, kvm)

		kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
@@ -2581,17 +2582,18 @@ u64 get_kvmclock_ns(struct kvm *kvm) 
{

	struct kvm_arch *ka = &kvm->arch;

	struct pvclock_vcpu_time_info hv_clock;

	unsigned long flags;

	u64 ret;



	spin_lock(&ka->pvclock_gtod_sync_lock);

	spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags);

	if (!ka->use_master_clock) {

		spin_unlock(&ka->pvclock_gtod_sync_lock);

		spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags);

		return get_kvmclock_base_ns() + ka->kvmclock_offset;

	}



	hv_clock.tsc_timestamp = ka->master_cycle_now;

	hv_clock.system_time = ka->master_kernel_ns + ka->kvmclock_offset;

	spin_unlock(&ka->pvclock_gtod_sync_lock);

	spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags);



	/* both __this_cpu_read() and rdtsc() should be on the same cpu */

	get_cpu();
@@ -2685,13 +2687,13 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) 
	 * If the host uses TSC clock, then passthrough TSC as stable

	 * to the guest.

	 */

	spin_lock(&ka->pvclock_gtod_sync_lock);

	spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags);

	use_master_clock = ka->use_master_clock;

	if (use_master_clock) {

		host_tsc = ka->master_cycle_now;

		kernel_ns = ka->master_kernel_ns;

	}

	spin_unlock(&ka->pvclock_gtod_sync_lock);

	spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags);



	/* Keep irq disabled to prevent changes to the clock */

	local_irq_save(flags);
@@ -7723,6 +7725,7 @@ static void kvm_hyperv_tsc_notifier(void) 
	struct kvm *kvm;

	struct kvm_vcpu *vcpu;

	int cpu;

	unsigned long flags;



	mutex_lock(&kvm_lock);

	list_for_each_entry(kvm, &vm_list, vm_list)
@@ -7738,9 +7741,9 @@ static void kvm_hyperv_tsc_notifier(void) 
	list_for_each_entry(kvm, &vm_list, vm_list) {

		struct kvm_arch *ka = &kvm->arch;



		spin_lock(&ka->pvclock_gtod_sync_lock);

		spin_lock_irqsave(&ka->pvclock_gtod_sync_lock, flags);

		pvclock_update_vm_gtod_copy(kvm);

		spin_unlock(&ka->pvclock_gtod_sync_lock);

		spin_unlock_irqrestore(&ka->pvclock_gtod_sync_lock, flags);



		kvm_for_each_vcpu(cpu, vcpu, kvm)

			kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);