KVM: nVMX: Prepare for using hardware MSR bitmap

Currently, if L1 enables MSR_BITMAP, we will emulate this feature, all
of L2's msr access is intercepted by L0.  Features like "virtualize
x2apic mode" require that the MSR bitmap is enabled, or the hardware
will exit and for example not virtualize the x2apic MSRs.  In order to
let L1 use these features, we need to build a merged bitmap that only
not cause a VMEXIT if 1) L1 requires that 2) the bit is not required by
the processor for APIC virtualization.

For now the guests are still run with MSR bitmap disabled, but this
patch already introduces nested_vmx_merge_msr_bitmap for future use.
Signed-off-by: Wincy Van <fanwenyi0529@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

@@ -800,6 +800,7 @@ static unsigned long *vmx_msr_bitmap_legacy;
 static unsigned long *vmx_msr_bitmap_longmode;
 static unsigned long *vmx_msr_bitmap_legacy_x2apic;
 static unsigned long *vmx_msr_bitmap_longmode_x2apic;
+static unsigned long *vmx_msr_bitmap_nested;
 static unsigned long *vmx_vmread_bitmap;
 static unsigned long *vmx_vmwrite_bitmap;
 
@@ -5823,13 +5824,21 @@ static __init int hardware_setup(void)
 				(unsigned long *)__get_free_page(GFP_KERNEL);
 	if (!vmx_msr_bitmap_longmode_x2apic)
 		goto out4;
+
+	if (nested) {
+		vmx_msr_bitmap_nested =
+			(unsigned long *)__get_free_page(GFP_KERNEL);
+		if (!vmx_msr_bitmap_nested)
+			goto out5;
+	}
+
 	vmx_vmread_bitmap = (unsigned long *)__get_free_page(GFP_KERNEL);
 	if (!vmx_vmread_bitmap)
-		goto out5;
+		goto out6;
 
 	vmx_vmwrite_bitmap = (unsigned long *)__get_free_page(GFP_KERNEL);
 	if (!vmx_vmwrite_bitmap)
-		goto out6;
+		goto out7;
 
 	memset(vmx_vmread_bitmap, 0xff, PAGE_SIZE);
 	memset(vmx_vmwrite_bitmap, 0xff, PAGE_SIZE);
@@ -5845,10 +5854,12 @@ static __init int hardware_setup(void)
 
 	memset(vmx_msr_bitmap_legacy, 0xff, PAGE_SIZE);
 	memset(vmx_msr_bitmap_longmode, 0xff, PAGE_SIZE);
+	if (nested)
+		memset(vmx_msr_bitmap_nested, 0xff, PAGE_SIZE);
 
 	if (setup_vmcs_config(&vmcs_config) < 0) {
 		r = -EIO;
-		goto out7;
+		goto out8;
 	}
 
 	if (boot_cpu_has(X86_FEATURE_NX))
@@ -5968,10 +5979,13 @@ static __init int hardware_setup(void)
 
 	return alloc_kvm_area();
 
-out7:
+out8:
 	free_page((unsigned long)vmx_vmwrite_bitmap);
-out6:
+out7:
 	free_page((unsigned long)vmx_vmread_bitmap);
+out6:
+	if (nested)
+		free_page((unsigned long)vmx_msr_bitmap_nested);
 out5:
 	free_page((unsigned long)vmx_msr_bitmap_longmode_x2apic);
 out4:
@@ -5998,6 +6012,8 @@ static __exit void hardware_unsetup(void)
 	free_page((unsigned long)vmx_io_bitmap_a);
 	free_page((unsigned long)vmx_vmwrite_bitmap);
 	free_page((unsigned long)vmx_vmread_bitmap);
+	if (nested)
+		free_page((unsigned long)vmx_msr_bitmap_nested);
 
 	free_kvm_area();
 }
@@ -8455,6 +8471,38 @@ static void vmx_start_preemption_timer(struct kvm_vcpu *vcpu)
 		      ns_to_ktime(preemption_timeout), HRTIMER_MODE_REL);
 }
 
+static int nested_vmx_check_msr_bitmap_controls(struct kvm_vcpu *vcpu,
+						struct vmcs12 *vmcs12)
+{
+	int maxphyaddr;
+	u64 addr;
+
+	if (!nested_cpu_has(vmcs12, CPU_BASED_USE_MSR_BITMAPS))
+		return 0;
+
+	if (vmcs12_read_any(vcpu, MSR_BITMAP, &addr)) {
+		WARN_ON(1);
+		return -EINVAL;
+	}
+	maxphyaddr = cpuid_maxphyaddr(vcpu);
+
+	if (!PAGE_ALIGNED(vmcs12->msr_bitmap) ||
+	   ((addr + PAGE_SIZE) >> maxphyaddr))
+		return -EINVAL;
+
+	return 0;
+}
+
+/*
+ * Merge L0's and L1's MSR bitmap, return false to indicate that
+ * we do not use the hardware.
+ */
+static inline bool nested_vmx_merge_msr_bitmap(struct kvm_vcpu *vcpu,
+					       struct vmcs12 *vmcs12)
+{
+	return false;
+}
+
 static int nested_vmx_check_msr_switch(struct kvm_vcpu *vcpu,
 				       unsigned long count_field,
 				       unsigned long addr_field,
@@ -8787,11 +8835,17 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 		vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);
 	}
 
+	if (cpu_has_vmx_msr_bitmap() &&
+	    exec_control & CPU_BASED_USE_MSR_BITMAPS &&
+	    nested_vmx_merge_msr_bitmap(vcpu, vmcs12)) {
+		vmcs_write64(MSR_BITMAP, __pa(vmx_msr_bitmap_nested));
+	} else
+		exec_control &= ~CPU_BASED_USE_MSR_BITMAPS;
+
 	/*
-	 * Merging of IO and MSR bitmaps not currently supported.
+	 * Merging of IO bitmap not currently supported.
 	 * Rather, exit every time.
 	 */
-	exec_control &= ~CPU_BASED_USE_MSR_BITMAPS;
 	exec_control &= ~CPU_BASED_USE_IO_BITMAPS;
 	exec_control |= CPU_BASED_UNCOND_IO_EXITING;
 
@@ -8942,15 +8996,13 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 		return 1;
 	}
 
-	if ((vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_MSR_BITMAPS) &&
-			!PAGE_ALIGNED(vmcs12->msr_bitmap)) {
+	if (!nested_get_vmcs12_pages(vcpu, vmcs12)) {
 		/*TODO: Also verify bits beyond physical address width are 0*/
 		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
 		return 1;
 	}
 
-	if (!nested_get_vmcs12_pages(vcpu, vmcs12)) {
-		/*TODO: Also verify bits beyond physical address width are 0*/
+	if (nested_vmx_check_msr_bitmap_controls(vcpu, vmcs12)) {
 		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
 		return 1;
 	}
@@ -9506,6 +9558,9 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
 	kvm_set_dr(vcpu, 7, 0x400);
 	vmcs_write64(GUEST_IA32_DEBUGCTL, 0);
 
+	if (cpu_has_vmx_msr_bitmap())
+		vmx_set_msr_bitmap(vcpu);
+
 	if (nested_vmx_load_msr(vcpu, vmcs12->vm_exit_msr_load_addr,
 				vmcs12->vm_exit_msr_load_count))
 		nested_vmx_abort(vcpu, VMX_ABORT_LOAD_HOST_MSR_FAIL);