KVM: x86: update masterclock when kvmclock_offset is calculated (v2)

The offset to add to the hosts monotonic time, kvmclock_offset, is
calculated against the monotonic time at KVM_SET_CLOCK ioctl time.

Request a master clock update at this time, to reduce a potentially
unbounded difference between the values of the masterclock and
the clock value used to calculate kvmclock_offset.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e514b3c..e5ca72a 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1447,6 +1447,29 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm)
 #endif
 }
 
+static void kvm_gen_update_masterclock(struct kvm *kvm)
+{
+#ifdef CONFIG_X86_64
+       int i;
+       struct kvm_vcpu *vcpu;
+       struct kvm_arch *ka = &kvm->arch;
+
+       spin_lock(&ka->pvclock_gtod_sync_lock);
+       kvm_make_mclock_inprogress_request(kvm);
+       /* no guest entries from this point */
+       pvclock_update_vm_gtod_copy(kvm);
+
+       kvm_for_each_vcpu(i, vcpu, kvm)
+               set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests);
+
+       /* guest entries allowed */
+       kvm_for_each_vcpu(i, vcpu, kvm)
+               clear_bit(KVM_REQ_MCLOCK_INPROGRESS, &vcpu->requests);
+
+       spin_unlock(&ka->pvclock_gtod_sync_lock);
+#endif
+}
+
 static int kvm_guest_time_update(struct kvm_vcpu *v)
 {
        unsigned long flags, this_tsc_khz;
@@ -3796,6 +3819,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
                delta = user_ns.clock - now_ns;
                local_irq_enable();
                kvm->arch.kvmclock_offset = delta;
+               kvm_gen_update_masterclock(kvm);
                break;
        }
        case KVM_GET_CLOCK: {
@@ -5804,29 +5828,6 @@ static void process_nmi(struct kvm_vcpu *vcpu)
        kvm_make_request(KVM_REQ_EVENT, vcpu);
 }
 
-static void kvm_gen_update_masterclock(struct kvm *kvm)
-{
-#ifdef CONFIG_X86_64
-       int i;
-       struct kvm_vcpu *vcpu;
-       struct kvm_arch *ka = &kvm->arch;
-
-       spin_lock(&ka->pvclock_gtod_sync_lock);
-       kvm_make_mclock_inprogress_request(kvm);
-       /* no guest entries from this point */
-       pvclock_update_vm_gtod_copy(kvm);
-
-       kvm_for_each_vcpu(i, vcpu, kvm)
-               set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests);
-
-       /* guest entries allowed */
-       kvm_for_each_vcpu(i, vcpu, kvm)
-               clear_bit(KVM_REQ_MCLOCK_INPROGRESS, &vcpu->requests);
-
-       spin_unlock(&ka->pvclock_gtod_sync_lock);
-#endif
-}
-
 static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
 {
        u64 eoi_exit_bitmap[4];