KVM: nVMX: nested TPR shadow/threshold emulation

This patch fix bug https://bugzilla.kernel.org/show_bug.cgi?id=61411

TPR shadow/threshold feature is important to speed up the Windows guest.
Besides, it is a must feature for certain VMM.

We map virtual APIC page address and TPR threshold from L1 VMCS. If
TPR_BELOW_THRESHOLD VM exit is triggered by L2 guest and L1 interested
in, we inject it into L1 VMM for handling.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
[Add PAGE_ALIGNED check, do not write useless virtual APIC page address
 if TPR shadowing is disabled. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

@@ -397,6 +397,7 @@ struct nested_vmx {
 	 * we must keep them pinned while L2 runs.
 	 */
 	struct page *apic_access_page;
+	struct page *virtual_apic_page;
 	u64 msr_ia32_feature_control;
 
 	struct hrtimer preemption_timer;
@@ -555,6 +556,7 @@ static int max_shadow_read_only_fields =
 	ARRAY_SIZE(shadow_read_only_fields);
 
 static unsigned long shadow_read_write_fields[] = {
+	TPR_THRESHOLD,
 	GUEST_RIP,
 	GUEST_RSP,
 	GUEST_CR0,
@@ -2352,7 +2354,7 @@ static __init void nested_vmx_setup_ctls_msrs(void)
 		CPU_BASED_MOV_DR_EXITING | CPU_BASED_UNCOND_IO_EXITING |
 		CPU_BASED_USE_IO_BITMAPS | CPU_BASED_MONITOR_EXITING |
 		CPU_BASED_RDPMC_EXITING | CPU_BASED_RDTSC_EXITING |
-		CPU_BASED_PAUSE_EXITING |
+		CPU_BASED_PAUSE_EXITING | CPU_BASED_TPR_SHADOW |
 		CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
 	/*
 	 * We can allow some features even when not supported by the
@@ -6246,6 +6248,10 @@ static void free_nested(struct vcpu_vmx *vmx)
 		nested_release_page(vmx->nested.apic_access_page);
 		vmx->nested.apic_access_page = 0;
 	}
+	if (vmx->nested.virtual_apic_page) {
+		nested_release_page(vmx->nested.virtual_apic_page);
+		vmx->nested.virtual_apic_page = 0;
+	}
 
 	nested_free_all_saved_vmcss(vmx);
 }
@@ -7034,7 +7040,7 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
 	case EXIT_REASON_MCE_DURING_VMENTRY:
 		return 0;
 	case EXIT_REASON_TPR_BELOW_THRESHOLD:
-		return 1;
+		return nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW);
 	case EXIT_REASON_APIC_ACCESS:
 		return nested_cpu_has2(vmcs12,
 			SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES);
@@ -7155,6 +7161,12 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 
 static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
 {
+	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
+
+	if (is_guest_mode(vcpu) &&
+		nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW))
+		return;
+
 	if (irr == -1 || tpr < irr) {
 		vmcs_write32(TPR_THRESHOLD, 0);
 		return;
@@ -7933,8 +7945,8 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu,
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
 	if (nested_cpu_has2(vmcs12, SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
+		/* TODO: Also verify bits beyond physical address width are 0 */
 		if (!PAGE_ALIGNED(vmcs12->apic_access_addr))
-			/*TODO: Also verify bits beyond physical address width are 0*/
 			return false;
 
 		/*
@@ -7948,6 +7960,31 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu,
 		vmx->nested.apic_access_page =
 			nested_get_page(vcpu, vmcs12->apic_access_addr);
 	}
+
+	if (nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW)) {
+		/* TODO: Also verify bits beyond physical address width are 0 */
+		if (!PAGE_ALIGNED(vmcs12->virtual_apic_page_addr))
+			return false;
+
+		if (vmx->nested.virtual_apic_page) /* shouldn't happen */
+			nested_release_page(vmx->nested.virtual_apic_page);
+		vmx->nested.virtual_apic_page =
+			nested_get_page(vcpu, vmcs12->virtual_apic_page_addr);
+
+		/*
+		 * Failing the vm entry is _not_ what the processor does
+		 * but it's basically the only possibility we have.
+		 * We could still enter the guest if CR8 load exits are
+		 * enabled, CR8 store exits are enabled, and virtualize APIC
+		 * access is disabled; in this case the processor would never
+		 * use the TPR shadow and we could simply clear the bit from
+		 * the execution control.  But such a configuration is useless,
+		 * so let's keep the code simple.
+		 */
+		if (!vmx->nested.virtual_apic_page)
+			return false;
+	}
+
 	return true;
 }
 
@@ -8141,6 +8178,13 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	exec_control &= ~CPU_BASED_VIRTUAL_NMI_PENDING;
 	exec_control &= ~CPU_BASED_TPR_SHADOW;
 	exec_control |= vmcs12->cpu_based_vm_exec_control;
+
+	if (exec_control & CPU_BASED_TPR_SHADOW) {
+		vmcs_write64(VIRTUAL_APIC_PAGE_ADDR,
+				page_to_phys(vmx->nested.virtual_apic_page));
+		vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);
+	}
+
 	/*
 	 * Merging of IO and MSR bitmaps not currently supported.
 	 * Rather, exit every time.
@@ -8908,6 +8952,10 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
 		nested_release_page(vmx->nested.apic_access_page);
 		vmx->nested.apic_access_page = 0;
 	}
+	if (vmx->nested.virtual_apic_page) {
+		nested_release_page(vmx->nested.virtual_apic_page);
+		vmx->nested.virtual_apic_page = 0;
+	}
 
 	/*
 	 * Exiting from L2 to L1, we're now back to L1 which thinks it just