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: syzbot+b282b65c2c68492df769@syzkaller.appspotmail.com
Fixes: 30b5c851af79 ("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: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2301623..e1960ee 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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);