[PATCH v3 27/37] KVM: nVMX: Reload APIC access page on nested VM-Exit only if necessary

[Sean Christopherson]

Defer reloading L1's APIC page by logging the need for a reload and
processing it during nested VM-Exit instead of unconditionally reloading
the APIC page on nested VM-Exit.  This eliminates a TLB flush on the
majority of VM-Exits as the APIC page rarely needs to be reloaded.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
---
 arch/x86/kvm/vmx/nested.c |  9 ++++-----
 arch/x86/kvm/vmx/vmx.c    | 10 +++++++---
 arch/x86/kvm/vmx/vmx.h    |  1 +
 3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index e630d656b211..06fc0b68ecf3 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4367,11 +4367,10 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
 	kvm_vcpu_unmap(vcpu, &vmx->nested.pi_desc_map, true);
 	vmx->nested.pi_desc = NULL;
 
-	/*
-	 * We are now running in L2, mmu_notifier will force to reload the
-	 * page's hpa for L2 vmcs. Need to reload it for L1 before entering L1.
-	 */
-	kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
+	if (vmx->nested.reload_vmcs01_apic_access_page) {
+		vmx->nested.reload_vmcs01_apic_access_page = false;
+		kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
+	}
 
 	if ((exit_reason != -1) && (enable_shadow_vmcs || vmx->nested.hv_evmcs))
 		vmx->nested.need_vmcs12_to_shadow_sync = true;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ae7279802652..3155329bf844 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6138,10 +6138,14 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu)
 
 static void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu, hpa_t hpa)
 {
-	if (!is_guest_mode(vcpu)) {
-		vmcs_write64(APIC_ACCESS_ADDR, hpa);
-		vmx_flush_tlb_current(vcpu);
+	/* 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);
+	vmx_flush_tlb_current(vcpu);
 }
 
 static void vmx_hwapic_isr_update(struct kvm_vcpu *vcpu, int max_isr)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 571249e18bb6..66cc9f639e4b 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -138,6 +138,7 @@ struct nested_vmx {
 	bool vmcs02_initialized;
 
 	bool change_vmcs01_virtual_apic_mode;
+	bool reload_vmcs01_apic_access_page;
 
 	/*
 	 * Enlightened VMCS has been enabled. It does not mean that L1 has to
-- 
2.24.1