KVM: x86/xen: Use gfn_to_pfn_cache for vcpu_time_info

This switches the final pvclock to kvm_setup_pvclock_pfncache() and now
the old kvm_setup_pvclock_page() can be removed.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220303154127.202856-7-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -606,9 +606,8 @@ struct kvm_vcpu_hv {
 struct kvm_vcpu_xen {
 	u64 hypercall_rip;
 	u32 current_runstate;
-	bool vcpu_time_info_set;
 	struct gfn_to_pfn_cache vcpu_info_cache;
-	struct gfn_to_hva_cache vcpu_time_info_cache;
+	struct gfn_to_pfn_cache vcpu_time_info_cache;
 	struct gfn_to_pfn_cache runstate_cache;
 	u64 last_steal;
 	u64 runstate_entry_time;

arch/x86/kvm/x86.c

@@ -3011,65 +3011,6 @@ static void kvm_setup_guest_pvclock(struct kvm_vcpu *v,
 	trace_kvm_pvclock_update(v->vcpu_id, &vcpu->hv_clock);
 }
 
-static void kvm_setup_pvclock_page(struct kvm_vcpu *v,
-				   struct gfn_to_hva_cache *cache,
-				   unsigned int offset)
-{
-	struct kvm_vcpu_arch *vcpu = &v->arch;
-	struct pvclock_vcpu_time_info guest_hv_clock;
-
-	if (unlikely(kvm_read_guest_offset_cached(v->kvm, cache,
-		&guest_hv_clock, offset, sizeof(guest_hv_clock))))
-		return;
-
-	/* This VCPU is paused, but it's legal for a guest to read another
-	 * VCPU's kvmclock, so we really have to follow the specification where
-	 * it says that version is odd if data is being modified, and even after
-	 * it is consistent.
-	 *
-	 * Version field updates must be kept separate.  This is because
-	 * kvm_write_guest_cached might use a "rep movs" instruction, and
-	 * writes within a string instruction are weakly ordered.  So there
-	 * are three writes overall.
-	 *
-	 * As a small optimization, only write the version field in the first
-	 * and third write.  The vcpu->pv_time cache is still valid, because the
-	 * version field is the first in the struct.
-	 */
-	BUILD_BUG_ON(offsetof(struct pvclock_vcpu_time_info, version) != 0);
-
-	if (guest_hv_clock.version & 1)
-		++guest_hv_clock.version;  /* first time write, random junk */
-
-	vcpu->hv_clock.version = guest_hv_clock.version + 1;
-	kvm_write_guest_offset_cached(v->kvm, cache,
-				      &vcpu->hv_clock, offset,
-				      sizeof(vcpu->hv_clock.version));
-
-	smp_wmb();
-
-	/* retain PVCLOCK_GUEST_STOPPED if set in guest copy */
-	vcpu->hv_clock.flags |= (guest_hv_clock.flags & PVCLOCK_GUEST_STOPPED);
-
-	if (vcpu->pvclock_set_guest_stopped_request) {
-		vcpu->hv_clock.flags |= PVCLOCK_GUEST_STOPPED;
-		vcpu->pvclock_set_guest_stopped_request = false;
-	}
-
-	trace_kvm_pvclock_update(v->vcpu_id, &vcpu->hv_clock);
-
-	kvm_write_guest_offset_cached(v->kvm, cache,
-				      &vcpu->hv_clock, offset,
-				      sizeof(vcpu->hv_clock));
-
-	smp_wmb();
-
-	vcpu->hv_clock.version++;
-	kvm_write_guest_offset_cached(v->kvm, cache,
-				     &vcpu->hv_clock, offset,
-				     sizeof(vcpu->hv_clock.version));
-}
-
 static int kvm_guest_time_update(struct kvm_vcpu *v)
 {
 	unsigned long flags, tgt_tsc_khz;
@@ -3161,8 +3102,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 	if (vcpu->xen.vcpu_info_cache.active)
 		kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_info_cache,
 					offsetof(struct compat_vcpu_info, time));
-	if (vcpu->xen.vcpu_time_info_set)
-		kvm_setup_pvclock_page(v, &vcpu->xen.vcpu_time_info_cache, 0);
+	if (vcpu->xen.vcpu_time_info_cache.active)
+		kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0);
 	if (!v->vcpu_idx)
 		kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
 	return 0;

arch/x86/kvm/xen.c

@@ -463,25 +463,18 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 
 	case KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO:
 		if (data->u.gpa == GPA_INVALID) {
-			vcpu->arch.xen.vcpu_time_info_set = false;
+			kvm_gfn_to_pfn_cache_destroy(vcpu->kvm,
+						     &vcpu->arch.xen.vcpu_time_info_cache);
 			r = 0;
 			break;
 		}
 
-		/* It must fit within a single page */
-		if ((data->u.gpa & ~PAGE_MASK) + sizeof(struct pvclock_vcpu_time_info) > PAGE_SIZE) {
-			r = -EINVAL;
-			break;
-		}
-
-		r = kvm_gfn_to_hva_cache_init(vcpu->kvm,
+		r = kvm_gfn_to_pfn_cache_init(vcpu->kvm,
 					      &vcpu->arch.xen.vcpu_time_info_cache,
-					      data->u.gpa,
+					      NULL, KVM_HOST_USES_PFN, data->u.gpa,
 					      sizeof(struct pvclock_vcpu_time_info));
-		if (!r) {
-			vcpu->arch.xen.vcpu_time_info_set = true;
+		if (!r)
 			kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
-		}
 		break;
 
 	case KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADDR:
@@ -622,7 +615,7 @@ int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 		break;
 
 	case KVM_XEN_VCPU_ATTR_TYPE_VCPU_TIME_INFO:
-		if (vcpu->arch.xen.vcpu_time_info_set)
+		if (vcpu->arch.xen.vcpu_time_info_cache.active)
 			data->u.gpa = vcpu->arch.xen.vcpu_time_info_cache.gpa;
 		else
 			data->u.gpa = GPA_INVALID;
@@ -1066,4 +1059,6 @@ void kvm_xen_destroy_vcpu(struct kvm_vcpu *vcpu)
 				     &vcpu->arch.xen.runstate_cache);
 	kvm_gfn_to_pfn_cache_destroy(vcpu->kvm,
 				     &vcpu->arch.xen.vcpu_info_cache);
+	kvm_gfn_to_pfn_cache_destroy(vcpu->kvm,
+				     &vcpu->arch.xen.vcpu_time_info_cache);
 }