[RFC 2/2] KVM/nVMX: Add support for saving/restoring L2 meta-state stored by L0

[KarimAllah Ahmed <karahmed@amazon.de>]

Since L2 guest is running on L0 hypervisor directly, there is some state
that L0 holds that is needed to safely save/resume L2. The rest of the
state is constructed from the VMCS12 which is stored in the L1 hypervisor
memory.

NOTE: I am still debugging a VMEntry failure for L2 that occassionally
happens after a loop of save and restore.

Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
---
 arch/x86/include/asm/kvm_host.h |  3 +++
 arch/x86/include/uapi/asm/kvm.h |  7 +++++++
 arch/x86/kvm/vmx.c              | 44 +++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/x86.c              | 10 ++++++++++
 include/linux/kvm_host.h        |  2 ++
 include/uapi/linux/kvm.h        |  3 +++
 virt/kvm/kvm_main.c             | 24 ++++++++++++++++++++++
 7 files changed, 93 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2c8be56..4223ce9 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -966,6 +966,9 @@ struct kvm_x86_ops {
 	void (*vcpu_load)(struct kvm_vcpu *vcpu, int cpu);
 	void (*vcpu_put)(struct kvm_vcpu *vcpu);
 
+	int (*get_nested)(struct kvm_vcpu *vcpu, struct kvm_nested *nested);
+	int (*set_nested)(struct kvm_vcpu *vcpu, struct kvm_nested *nested);
+
 	void (*update_bp_intercept)(struct kvm_vcpu *vcpu);
 	int (*get_msr)(struct kvm_vcpu *vcpu, struct msr_data *msr);
 	int (*set_msr)(struct kvm_vcpu *vcpu, struct msr_data *msr);
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index b49816d..f1e36ef 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -157,6 +157,13 @@ struct kvm_sregs {
 	__u64 interrupt_bitmap[(KVM_NR_INTERRUPTS + 63) / 64];
 };
 
+struct kvm_nested {
+	__u8 vmxon;
+	__u64 vmxon_ptr;
+	__u64 current_vmptr;
+	__u64 vmcs01_debugctl;
+};
+
 /* for KVM_GET_FPU and KVM_SET_FPU */
 struct kvm_fpu {
 	__u8  fpr[8][16];
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 22eb0dc..813ca37 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -12419,6 +12419,47 @@ static int vmx_smi_allowed(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+static int vmx_set_nested(struct kvm_vcpu *vcpu, struct kvm_nested *nested)
+{
+	struct nested_vmx *nvmx = &to_vmx(vcpu)->nested;
+
+	if (!nested->vmxon)
+		return 0;
+
+	nvmx->vmxon_ptr = nested->vmxon_ptr;
+	enter_vmx_operation(vcpu);
+	nvmx->current_vmptr = nested->current_vmptr;
+	nvmx->vmcs01_debugctl = nested->vmcs01_debugctl;
+
+	if (nested->current_vmptr != -1ull) {
+		if (kvm_read_guest(vcpu->kvm, nvmx->current_vmptr,
+				   nvmx->cached_vmcs12,
+				   sizeof(*nvmx->cached_vmcs12)))
+			return -EFAULT;
+
+		set_current_vmptr(to_vmx(vcpu), nested->current_vmptr);
+	}
+
+	return 0;
+}
+
+static int vmx_get_nested(struct kvm_vcpu *vcpu, struct kvm_nested *nested)
+{
+	struct nested_vmx *nvmx = &to_vmx(vcpu)->nested;
+
+	memset(nested, 0, sizeof(*nested));
+
+	if (!nvmx->vmxon)
+		return 0;
+
+	nested->vmxon = true;
+	nested->vmxon_ptr = nvmx->vmxon_ptr;
+	nested->current_vmptr = nvmx->current_vmptr;
+	nested->vmcs01_debugctl = nvmx->vmcs01_debugctl;
+
+	return 0;
+}
+
 static int vmx_pre_enter_smm(struct kvm_vcpu *vcpu, char *smstate)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -12512,6 +12553,9 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
 
 	.tlb_flush = vmx_flush_tlb,
 
+	.set_nested = vmx_set_nested,
+	.get_nested = vmx_get_nested,
+
 	.run = vmx_vcpu_run,
 	.handle_exit = vmx_handle_exit,
 	.skip_emulated_instruction = skip_emulated_instruction,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8256a2d..de34a7a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7543,6 +7543,16 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	return r;
 }
 
+int kvm_arch_vcpu_ioctl_get_nested(struct kvm_vcpu *vcpu, struct kvm_nested *nested)
+{
+	return kvm_x86_ops->get_nested(vcpu, nested);
+}
+
+int kvm_arch_vcpu_ioctl_set_nested(struct kvm_vcpu *vcpu, struct kvm_nested *nested)
+{
+	return kvm_x86_ops->set_nested(vcpu, nested);
+}
+
 int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 {
 	vcpu_load(vcpu);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index beb9d42..becc066 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -776,6 +776,8 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu);
 int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
 				    struct kvm_translation *tr);
 
+int kvm_arch_vcpu_ioctl_get_nested(struct kvm_vcpu *vcpu, struct kvm_nested *nested);
+int kvm_arch_vcpu_ioctl_set_nested(struct kvm_vcpu *vcpu, struct kvm_nested *nested);
 int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs);
 int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs);
 int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 59e5b7b..eace4c8 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1467,6 +1467,9 @@ struct kvm_sev_dbg {
 	__u32 len;
 };
 
+#define KVM_GET_NESTED              _IOR(KVMIO,  0xba, struct kvm_nested)
+#define KVM_SET_NESTED              _IOW(KVMIO,  0xbb, struct kvm_nested)
+
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
 #define KVM_DEV_ASSIGN_MASK_INTX	(1 << 2)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 38f35ae..539ccfb 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2661,6 +2661,30 @@ static long kvm_vcpu_ioctl(struct file *filp,
 		kfree(kvm_regs);
 		break;
 	}
+	case KVM_GET_NESTED: {
+		struct kvm_nested nested;
+
+		r = kvm_arch_vcpu_ioctl_get_nested(vcpu, &nested);
+		if (r)
+			break;
+
+		r = -EFAULT;
+		if (copy_to_user(argp, &nested, sizeof(nested)))
+			break;
+
+		r = 0;
+		break;
+	}
+	case KVM_SET_NESTED: {
+		struct kvm_nested nested;
+
+		r = -EFAULT;
+		if (copy_from_user(&nested, argp, sizeof(nested)))
+			break;
+
+		r = kvm_arch_vcpu_ioctl_set_nested(vcpu, &nested);
+		break;
+	}
 	case KVM_GET_SREGS: {
 		kvm_sregs = kzalloc(sizeof(struct kvm_sregs), GFP_KERNEL);
 		r = -ENOMEM;
-- 
2.7.4