KVM: nVMX: Use kvm_{read,write}_guest_cached() for shadow_vmcs12

Using kvm_vcpu_map() for reading from the guest is entirely gratuitous,
when all we do is a single memcpy and unmap it again. Fix it up to use
kvm_read_guest()... but in fact I couldn't bring myself to do that
without also making it use a gfn_to_hva_cache for both that *and* the
copy in the other direction.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20211115165030.7422-5-dwmw2@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -670,33 +670,39 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 static void nested_cache_shadow_vmcs12(struct kvm_vcpu *vcpu,
 				       struct vmcs12 *vmcs12)
 {
-	struct kvm_host_map map;
-	struct vmcs12 *shadow;
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct gfn_to_hva_cache *ghc = &vmx->nested.shadow_vmcs12_cache;
 
 	if (!nested_cpu_has_shadow_vmcs(vmcs12) ||
 	    vmcs12->vmcs_link_pointer == INVALID_GPA)
 		return;
 
-	shadow = get_shadow_vmcs12(vcpu);
-
-	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->vmcs_link_pointer), &map))
+	if (ghc->gpa != vmcs12->vmcs_link_pointer &&
+	    kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc,
+				      vmcs12->vmcs_link_pointer, VMCS12_SIZE))
 		return;
 
-	memcpy(shadow, map.hva, VMCS12_SIZE);
-	kvm_vcpu_unmap(vcpu, &map, false);
+	kvm_read_guest_cached(vmx->vcpu.kvm, ghc, get_shadow_vmcs12(vcpu),
+			      VMCS12_SIZE);
 }
 
 static void nested_flush_cached_shadow_vmcs12(struct kvm_vcpu *vcpu,
 					      struct vmcs12 *vmcs12)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct gfn_to_hva_cache *ghc = &vmx->nested.shadow_vmcs12_cache;
 
 	if (!nested_cpu_has_shadow_vmcs(vmcs12) ||
 	    vmcs12->vmcs_link_pointer == INVALID_GPA)
 		return;
 
-	kvm_write_guest(vmx->vcpu.kvm, vmcs12->vmcs_link_pointer,
-			get_shadow_vmcs12(vcpu), VMCS12_SIZE);
+	if (ghc->gpa != vmcs12->vmcs_link_pointer &&
+	    kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc,
+				      vmcs12->vmcs_link_pointer, VMCS12_SIZE))
+		return;
+
+	kvm_write_guest_cached(vmx->vcpu.kvm, ghc, get_shadow_vmcs12(vcpu),
+			       VMCS12_SIZE);
 }
 
 /*

arch/x86/kvm/vmx/vmx.h

@@ -141,6 +141,11 @@ struct nested_vmx {
 	 */
 	struct vmcs12 *cached_shadow_vmcs12;
 
+	/*
+	 * GPA to HVA cache for accessing vmcs12->vmcs_link_pointer
+	 */
+	struct gfn_to_hva_cache shadow_vmcs12_cache;
+
 	/*
 	 * Indicates if the shadow vmcs or enlightened vmcs must be updated
 	 * with the data held by struct vmcs12.