1 files changed, 44 insertions, 20 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a83ca63d26fc..64c5dc37c6a1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -719,6 +719,24 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
 }
 
 /*
+ * KVM_SET_USER_MEMORY_REGION ioctl allows the following operations:
+ * - create a new memory slot
+ * - delete an existing memory slot
+ * - modify an existing memory slot
+ *   -- move it in the guest physical memory space
+ *   -- just change its flags
+ *
+ * Since flags can be changed by some of these operations, the following
+ * differentiation is the best we can do for __kvm_set_memory_region():
+ */
+enum kvm_mr_change {
+        KVM_MR_CREATE,
+        KVM_MR_DELETE,
+        KVM_MR_MOVE,
+        KVM_MR_FLAGS_ONLY,
+};
+
+/*
  * Allocate some memory and give it an address in the guest physical address
  * space.
  *
@@ -737,6 +755,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
         struct kvm_memory_slot old, new;
         struct kvm_memslots *slots = NULL, *old_memslots;
         bool old_iommu_mapped;
+        enum kvm_mr_change change;
 
         r = check_memory_region_flags(mem);
         if (r)
@@ -780,17 +799,30 @@ int __kvm_set_memory_region(struct kvm *kvm,
 
         old_iommu_mapped = old.npages;
 
-        /*
-         * Disallow changing a memory slot's size or changing anything about
-         * zero sized slots that doesn't involve making them non-zero.
-         */
         r = -EINVAL;
-        if (npages && old.npages && npages != old.npages)
-                goto out;
-        if (!npages && !old.npages)
+        if (npages) {
+                if (!old.npages)
+                        change = KVM_MR_CREATE;
+                else { /* Modify an existing slot. */
+                        if ((mem->userspace_addr != old.userspace_addr) ||
+                            (npages != old.npages))
+                                goto out;
+
+                        if (base_gfn != old.base_gfn)
+                                change = KVM_MR_MOVE;
+                        else if (new.flags != old.flags)
+                                change = KVM_MR_FLAGS_ONLY;
+                        else { /* Nothing to change. */
+                                r = 0;
+                                goto out;
+                        }
+                }
+        } else if (old.npages) {
+                change = KVM_MR_DELETE;
+        } else /* Modify a non-existent slot: disallowed. */
                 goto out;
 
-        if ((npages && !old.npages) || (base_gfn != old.base_gfn)) {
+        if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
                 /* Check for overlaps */
                 r = -EEXIST;
                 kvm_for_each_memslot(slot, kvm->memslots) {
@@ -808,20 +840,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 new.dirty_bitmap = NULL;
 
         r = -ENOMEM;
-
-        /*
-         * Allocate if a slot is being created.  If modifying a slot,
-         * the userspace_addr cannot change.
-         */
-        if (!old.npages) {
+        if (change == KVM_MR_CREATE) {
                 new.user_alloc = user_alloc;
                 new.userspace_addr = mem->userspace_addr;
 
                 if (kvm_arch_create_memslot(&new, npages))
                         goto out_free;
-        } else if (npages && mem->userspace_addr != old.userspace_addr) {
-                r = -EINVAL;
-                goto out_free;
         }
 
         /* Allocate page dirty bitmap if needed */
@@ -830,7 +854,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
                         goto out_free;
         }
 
-        if (!npages || base_gfn != old.base_gfn) {
+        if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
                 r = -ENOMEM;
                 slots = kmemdup(kvm->memslots, sizeof(struct kvm_memslots),
                                 GFP_KERNEL);
@@ -881,7 +905,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
          * slots (size changes, userspace addr changes) is disallowed above,
          * so any other attribute changes getting here can be skipped.
          */
-        if (npages) {
+        if (change != KVM_MR_DELETE) {
                 if (old_iommu_mapped &&
                     ((new.flags ^ old.flags) & KVM_MEM_READONLY)) {
                         kvm_iommu_unmap_pages(kvm, &old);
@@ -896,7 +920,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
         }
 
         /* actual memory is freed via old in kvm_free_physmem_slot below */
-        if (!npages) {
+        if (change == KVM_MR_DELETE) {
                 new.dirty_bitmap = NULL;
                 memset(&new.arch, 0, sizeof(new.arch));
         }