KVM: nSVM: implement on demand allocation of the nested state

This way we don't waste memory on VMs which don't use nesting
virtualization even when the host enabled it for them.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201001112954.6258-5-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index ba50ff6e35c7..9e4c226dbf7d 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -481,6 +481,9 @@ int nested_svm_vmrun(struct vcpu_svm *svm)
 
 	vmcb12 = map.hva;
 
+	if (WARN_ON_ONCE(!svm->nested.initialized))
+		return -EINVAL;
+
 	if (!nested_vmcb_checks(svm, vmcb12)) {
 		vmcb12->control.exit_code    = SVM_EXIT_ERR;
 		vmcb12->control.exit_code_hi = 0;
@@ -698,6 +701,45 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	return 0;
 }
 
+int svm_allocate_nested(struct vcpu_svm *svm)
+{
+	struct page *hsave_page;
+
+	if (svm->nested.initialized)
+		return 0;
+
+	hsave_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
+	if (!hsave_page)
+		return -ENOMEM;
+	svm->nested.hsave = page_address(hsave_page);
+
+	svm->nested.msrpm = svm_vcpu_alloc_msrpm();
+	if (!svm->nested.msrpm)
+		goto err_free_hsave;
+	svm_vcpu_init_msrpm(&svm->vcpu, svm->nested.msrpm);
+
+	svm->nested.initialized = true;
+	return 0;
+
+err_free_hsave:
+	__free_page(hsave_page);
+	return -ENOMEM;
+}
+
+void svm_free_nested(struct vcpu_svm *svm)
+{
+	if (!svm->nested.initialized)
+		return;
+
+	svm_vcpu_free_msrpm(svm->nested.msrpm);
+	svm->nested.msrpm = NULL;
+
+	__free_page(virt_to_page(svm->nested.hsave));
+	svm->nested.hsave = NULL;
+
+	svm->nested.initialized = false;
+}
+
 /*
  * Forcibly leave nested mode in order to be able to reset the VCPU later on.
  */