[PATCH 8/24] Hold a vmcs02 for each vmcs12

["Nadav Har'El" <nyh@il.ibm.com>]

In this patch we add a list of L0 (hardware) VMCSs, which we'll use to hold a 
hardware VMCS for each active L1 VMCS (i.e., for each L2 guest).

We call each of these L0 VMCSs a "vmcs02", as it is the VMCS that L0 uses
to run its nested guest L2.

Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
---
--- .before/arch/x86/kvm/vmx.c	2010-06-13 15:01:29.000000000 +0300
+++ .after/arch/x86/kvm/vmx.c	2010-06-13 15:01:29.000000000 +0300
@@ -140,6 +140,12 @@ struct __attribute__ ((__packed__)) vmcs
 	u32 abort;
 };
 
+struct vmcs_list {
+	struct list_head list;
+	gpa_t vmcs_addr;
+	struct vmcs *l2_vmcs;
+};
+
 /* The nested_vmx structure is part of vcpu_vmx, and holds information we need
  * for correct emulation of VMX (i.e., nested VMX) on this vcpu. For example,
  * the current VMCS set by L1, a list of the VMCSs used to run the active
@@ -153,6 +159,10 @@ struct nested_vmx {
 	gpa_t current_vmptr;
 	/* The host-usable pointer to the above. Set by nested_map_current() */
 	struct vmcs12 *current_l2_page;
+
+	/* list of real (hardware) VMCS, one for each L2 guest of L1 */
+	struct list_head l2_vmcs_list; /* a vmcs_list */
+	int l2_vmcs_num;
 };
 
 struct vcpu_vmx {
@@ -1754,6 +1764,84 @@ static void free_vmcs(struct vmcs *vmcs)
 	free_pages((unsigned long)vmcs, vmcs_config.order);
 }
 
+static struct vmcs *nested_get_current_vmcs(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct vmcs_list *list_item, *n;
+
+	list_for_each_entry_safe(list_item, n, &vmx->nested.l2_vmcs_list, list)
+		if (list_item->vmcs_addr == vmx->nested.current_vmptr)
+			return list_item->l2_vmcs;
+
+	return NULL;
+}
+
+/* Allocate an L0 VMCS (vmcs02) for the current L1 VMCS (vmcs12), if one
+ * does not already exist. The allocation is done in L0 memory, so to avoid
+ * denial-of-service attack by guests, we limit the number of concurrently-
+ * allocated vmcss. A well-behaving L1 will VMCLEAR unused vmcs12s and not
+ * trigger this limit.
+ */
+static const int NESTED_MAX_VMCS = 256;
+static int nested_create_current_vmcs(struct kvm_vcpu *vcpu)
+{
+	struct vmcs_list *new_l2_guest;
+	struct vmcs *l2_vmcs;
+
+	if (nested_get_current_vmcs(vcpu))
+		return 0; /* nothing to do - we already have a VMCS */
+
+	if (to_vmx(vcpu)->nested.l2_vmcs_num >= NESTED_MAX_VMCS)
+		return -ENOMEM;
+
+	new_l2_guest = (struct vmcs_list *)
+		kmalloc(sizeof(struct vmcs_list), GFP_KERNEL);
+	if (!new_l2_guest)
+		return -ENOMEM;
+
+	l2_vmcs = alloc_vmcs();
+	if (!l2_vmcs) {
+		kfree(new_l2_guest);
+		return -ENOMEM;
+	}
+
+	new_l2_guest->vmcs_addr = to_vmx(vcpu)->nested.current_vmptr;
+	new_l2_guest->l2_vmcs = l2_vmcs;
+	list_add(&(new_l2_guest->list), &(to_vmx(vcpu)->nested.l2_vmcs_list));
+	to_vmx(vcpu)->nested.l2_vmcs_num++;
+	return 0;
+}
+
+/* Free the current L2 VMCS, and remove it from l2_vmcs_list */
+static void nested_free_current_vmcs(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct vmcs_list *list_item, *n;
+
+	list_for_each_entry_safe(list_item, n, &vmx->nested.l2_vmcs_list, list)
+		if (list_item->vmcs_addr == vmx->nested.current_vmptr) {
+			free_vmcs(list_item->l2_vmcs);
+			list_del(&(list_item->list));
+			kfree(list_item);
+			vmx->nested.l2_vmcs_num--;
+			return;
+		}
+}
+
+static void free_l1_state(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct vmcs_list *list_item, *n;
+
+	list_for_each_entry_safe(list_item, n,
+			&vmx->nested.l2_vmcs_list, list) {
+		free_vmcs(list_item->l2_vmcs);
+		list_del(&(list_item->list));
+		kfree(list_item);
+	}
+	vmx->nested.l2_vmcs_num = 0;
+}
+
 static void free_kvm_area(void)
 {
 	int cpu;
@@ -3606,6 +3694,9 @@ static int handle_vmon(struct kvm_vcpu *
 		return 1;
 	}
 
+	INIT_LIST_HEAD(&(vmx->nested.l2_vmcs_list));
+	vmx->nested.l2_vmcs_num = 0;
+
 	vmx->nested.vmxon = 1;
 
 	skip_emulated_instruction(vcpu);
@@ -3650,6 +3741,8 @@ static int handle_vmoff(struct kvm_vcpu 
 
 	to_vmx(vcpu)->nested.vmxon = 0;
 
+	free_l1_state(vcpu);
+
 	skip_emulated_instruction(vcpu);
 	return 1;
 }
@@ -4402,6 +4495,8 @@ static void vmx_free_vcpu(struct kvm_vcp
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
 	free_vpid(vmx);
+	if (vmx->nested.vmxon)
+		free_l1_state(vcpu);
 	vmx_free_vmcs(vcpu);
 	kfree(vmx->guest_msrs);
 	kvm_vcpu_uninit(vcpu);