[RFC 3/8] always call kvm_write_guest

[Glauber Costa <glommer@redhat.com>]

This patch makes sure that kvm_write_guest() is called
at every guest enter. We do not, however, want to update
all the structure at all times, so we add a flag
that basically tells it whether or not to do the whole operation

Signed-off-by: Glauber Costa <glommer@redhat.com>
---
 arch/x86/kvm/x86.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e7e3b50..f4b77ea 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -895,7 +895,7 @@ static void kvm_set_time_scale(uint32_t tsc_khz, struct pvclock_vcpu_time_info *
 
 static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
 
-static void kvm_write_guest_time(struct kvm_vcpu *v)
+static void kvm_write_guest_time(struct kvm_vcpu *v, bool update_time)
 {
 	struct timespec ts;
 	unsigned long flags;
@@ -906,6 +906,9 @@ static void kvm_write_guest_time(struct kvm_vcpu *v)
 	if ((!vcpu->time_page))
 		return;
 
+	if (!update_time)
+		return;
+
 	this_tsc_khz = get_cpu_var(cpu_tsc_khz);
 	if (unlikely(vcpu->hv_clock_tsc_khz != this_tsc_khz)) {
 		kvm_set_time_scale(this_tsc_khz, &vcpu->hv_clock);
@@ -4671,6 +4674,7 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
 static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 {
 	int r;
+	bool update_kvm_time = 0;
 	bool req_int_win = !irqchip_in_kernel(vcpu->kvm) &&
 		vcpu->run->request_interrupt_window;
 
@@ -4680,7 +4684,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
 			__kvm_migrate_timers(vcpu);
 		if (kvm_check_request(KVM_REQ_KVMCLOCK_UPDATE, vcpu))
-			kvm_write_guest_time(vcpu);
+			update_kvm_time = 1;
 		if (kvm_check_request(KVM_REQ_MMU_SYNC, vcpu))
 			kvm_mmu_sync_roots(vcpu);
 		if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu))
@@ -4701,6 +4705,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		}
 	}
 
+	kvm_write_guest_time(vcpu, update_kvm_time);
+
 	r = kvm_mmu_reload(vcpu);
 	if (unlikely(r))
 		goto out;
-- 
1.6.2.2