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>

1 files changed, 24 insertions, 23 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e514b3cb8b93..e5ca72a5cdb6 100644
--- 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];