kvm: Fix memory slot generation updates

Previous patch "kvm: Minor memory slot optimization" (b7f69c555ca43)
overlooked the generation field of the memory slots.  Re-using the
original memory slots left us with with two slightly different memory
slots with the same generation.  To fix this, make update_memslots()
take a new parameter to specify the last generation.  This also makes
generation management more explicit to avoid such problems in the future.

Reported-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index bd31096e3698..14cbae83be64 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -672,7 +672,8 @@ static void sort_memslots(struct kvm_memslots *slots)
                 slots->id_to_index[slots->memslots[i].id] = i;
 }
 
-void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new)
+void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new,
+                     u64 last_generation)
 {
         if (new) {
                 int id = new->id;
@@ -684,7 +685,7 @@ void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new)
                         sort_memslots(slots);
         }
 
-        slots->generation++;
+        slots->generation = last_generation + 1;
 }
 
 static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
@@ -819,7 +820,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 slot = id_to_memslot(slots, mem->slot);
                 slot->flags |= KVM_MEMSLOT_INVALID;
 
-                update_memslots(slots, NULL);
+                update_memslots(slots, NULL, kvm->memslots->generation);
 
                 old_memslots = kvm->memslots;
                 rcu_assign_pointer(kvm->memslots, slots);
@@ -867,7 +868,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 memset(&new.arch, 0, sizeof(new.arch));
         }
 
-        update_memslots(slots, &new);
+        update_memslots(slots, &new, kvm->memslots->generation);
         old_memslots = kvm->memslots;
         rcu_assign_pointer(kvm->memslots, slots);
         synchronize_srcu_expedited(&kvm->srcu);