Disallow the deletion of memory slots (and aliases, for x86 case), if a
vcpu contains a cr3 that points to such slot/alias.

This complements commit 6c20e1442bb1c62914bb85b7f4a38973d2a423ba.

v2:
- set KVM_REQ_TRIPLE_FAULT
- use __KVM_HAVE_ARCH_CAN_FREE_MEMSLOT to avoid duplication of stub

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm-pending/arch/x86/kvm/x86.c
===================================================================
--- kvm-pending.orig/arch/x86/kvm/x86.c
+++ kvm-pending/arch/x86/kvm/x86.c
@@ -1636,6 +1636,29 @@ gfn_t unalias_gfn(struct kvm *kvm, gfn_t
 	return gfn;
 }
 
+static int kvm_root_gfn_in_range(struct kvm *kvm, gfn_t base_gfn,
+				 gfn_t end_gfn, bool unalias)
+{
+	struct kvm_vcpu *vcpu;
+	gfn_t root_gfn;
+	int i;
+
+	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
+		vcpu = kvm->vcpus[i];
+		if (!vcpu)
+			continue;
+		root_gfn = vcpu->arch.cr3 >> PAGE_SHIFT;
+		if (unalias)
+			root_gfn = unalias_gfn(kvm, root_gfn);
+		if (root_gfn >= base_gfn && root_gfn <= end_gfn) {
+			set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
 /*
  * Set a new alias region.  Aliases map a portion of physical memory into
  * another portion.  This is useful for memory windows, for example the PC
@@ -1666,6 +1689,19 @@ static int kvm_vm_ioctl_set_memory_alias
 	spin_lock(&kvm->mmu_lock);
 
 	p = &kvm->arch.aliases[alias->slot];
+
+	/* FIXME: either disallow shrinking alias slots or disable
+ 	 * size changes as done with memslots
+ 	 */
+	if (!alias->memory_size) {
+		r = -EBUSY;
+		if (kvm_root_gfn_in_range(kvm, p->base_gfn,
+					       p->base_gfn + p->npages - 1,
+					       false))
+			goto out_unlock;
+	}
+
+
 	p->base_gfn = alias->guest_phys_addr >> PAGE_SHIFT;
 	p->npages = alias->memory_size >> PAGE_SHIFT;
 	p->target_gfn = alias->target_phys_addr >> PAGE_SHIFT;
@@ -1682,6 +1718,9 @@ static int kvm_vm_ioctl_set_memory_alias
 
 	return 0;
 
+out_unlock:
+	spin_unlock(&kvm->mmu_lock);
+	up_write(&kvm->slots_lock);
 out:
 	return r;
 }
@@ -4552,6 +4591,15 @@ void kvm_arch_flush_shadow(struct kvm *k
 	kvm_mmu_zap_all(kvm);
 }
 
+int kvm_arch_can_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+	int ret;
+
+	ret = kvm_root_gfn_in_range(kvm, slot->base_gfn,
+				    slot->base_gfn + slot->npages - 1, true);
+	return !ret;
+}
+
 int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE
Index: kvm-pending/include/linux/kvm_host.h
===================================================================
--- kvm-pending.orig/include/linux/kvm_host.h
+++ kvm-pending/include/linux/kvm_host.h
@@ -200,6 +200,7 @@ int kvm_arch_set_memory_region(struct kv
 				struct kvm_memory_slot old,
 				int user_alloc);
 void kvm_arch_flush_shadow(struct kvm *kvm);
+int kvm_arch_can_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
 gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn);
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
 unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn);
Index: kvm-pending/virt/kvm/kvm_main.c
===================================================================
--- kvm-pending.orig/virt/kvm/kvm_main.c
+++ kvm-pending/virt/kvm/kvm_main.c
@@ -1061,6 +1061,13 @@ static int kvm_vm_release(struct inode *
 	return 0;
 }
 
+#ifndef __KVM_HAVE_ARCH_CAN_FREE_MEMSLOT
+int kvm_arch_can_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+	return 1;
+}
+#endif
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -1179,8 +1186,13 @@ int __kvm_set_memory_region(struct kvm *
 	}
 #endif /* not defined CONFIG_S390 */
 
-	if (!npages)
+	if (!npages) {
 		kvm_arch_flush_shadow(kvm);
+		if (!kvm_arch_can_free_memslot(kvm, memslot)) {
+			r = -EBUSY;
+			goto out_free;
+		}
+	}
 
 	spin_lock(&kvm->mmu_lock);
 	if (mem->slot >= kvm->nmemslots)
Index: kvm-pending/arch/x86/include/asm/kvm.h
===================================================================
--- kvm-pending.orig/arch/x86/include/asm/kvm.h
+++ kvm-pending/arch/x86/include/asm/kvm.h
@@ -18,6 +18,8 @@
 #define __KVM_HAVE_GUEST_DEBUG
 #define __KVM_HAVE_MSIX
 
+#define __KVM_HAVE_ARCH_CAN_FREE_MEMSLOT
+
 /* Architectural interrupt line count. */
 #define KVM_NR_INTERRUPTS 256