KVM: VMX: Retrieve APIC access page HPA only when necessary

Move the retrieval of the HPA associated with L1's APIC access page into
VMX code to avoid unnecessarily calling gfn_to_page(), e.g. when the
vCPU is in guest mode (L2).  Alternatively, the optimization logic in
VMX could be mirrored into the common x86 code, but that will get ugly
fast when further optimizations are introduced.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200320212833.3507-29-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1152,7 +1152,7 @@ struct kvm_x86_ops {
 	bool (*guest_apic_has_interrupt)(struct kvm_vcpu *vcpu);
 	void (*load_eoi_exitmap)(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap);
 	void (*set_virtual_apic_mode)(struct kvm_vcpu *vcpu);
-	void (*set_apic_access_page_addr)(struct kvm_vcpu *vcpu, hpa_t hpa);
+	void (*set_apic_access_page_addr)(struct kvm_vcpu *vcpu);
 	int (*deliver_posted_interrupt)(struct kvm_vcpu *vcpu, int vector);
 	int (*sync_pir_to_irr)(struct kvm_vcpu *vcpu);
 	int (*set_tss_addr)(struct kvm *kvm, unsigned int addr);

arch/x86/kvm/vmx/vmx.c

@@ -6140,16 +6140,28 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu)
 	vmx_update_msr_bitmap(vcpu);
 }
 
-static void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu, hpa_t hpa)
+static void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
 {
+	struct page *page;
+
 	/* Defer reload until vmcs01 is the current VMCS. */
 	if (is_guest_mode(vcpu)) {
 		to_vmx(vcpu)->nested.reload_vmcs01_apic_access_page = true;
 		return;
 	}
 
-	vmcs_write64(APIC_ACCESS_ADDR, hpa);
+	page = gfn_to_page(vcpu->kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
+	if (is_error_page(page))
+		return;
+
+	vmcs_write64(APIC_ACCESS_ADDR, page_to_phys(page));
 	vmx_flush_tlb_current(vcpu);
+
+	/*
+	 * Do not pin apic access page in memory, the MMU notifier
+	 * will call us again if it is migrated or swapped out.
+	 */
+	put_page(page);
 }
 
 static void vmx_hwapic_isr_update(struct kvm_vcpu *vcpu, int max_isr)

arch/x86/kvm/x86.c

@@ -8157,24 +8157,13 @@ int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
 
 void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
 {
-	struct page *page = NULL;
-
 	if (!lapic_in_kernel(vcpu))
 		return;
 
 	if (!kvm_x86_ops.set_apic_access_page_addr)
 		return;
 
-	page = gfn_to_page(vcpu->kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
-	if (is_error_page(page))
-		return;
-	kvm_x86_ops.set_apic_access_page_addr(vcpu, page_to_phys(page));
-
-	/*
-	 * Do not pin apic access page in memory, the MMU notifier
-	 * will call us again if it is migrated or swapped out.
-	 */
-	put_page(page);
+	kvm_x86_ops.set_apic_access_page_addr(vcpu);
 }
 
 void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu)