[PATCH] really remove a slow when a user ask us so

[Glauber Costa <glommer@redhat.com>]

Right now, KVM does not remove a slot when we do a
register ioctl for size 0 (would be the expected behaviour).

Instead, we only mark it as empty, but keep all bitmaps
and allocated data structures present. It completely
nullifies our chances of reusing that same slot again
for mapping a different piece of memory.

In this patch, we destroy rmaps, and vfree() the
pointers that used to hold the dirty bitmap, rmap
and lpage_info structures.

Signed-off-by: Glauber Costa <glommer@redhat.com>
---
 virt/kvm/kvm_main.c |   15 +++++++++------
 1 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b1953ee..f605bba 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -735,11 +735,17 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
 	npages = mem->memory_size >> PAGE_SHIFT;
 
-	if (!npages)
-		mem->flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
-
 	new = old = *memslot;
 
+        if (!npages) {
+                mem->flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
+                kvm_arch_flush_shadow(kvm);
+                kvm_free_physmem_slot(memslot, NULL);
+                kvm_arch_set_memory_region(kvm, mem, old, user_alloc);
+                goto out;
+        }
+
+
 	new.base_gfn = base_gfn;
 	new.npages = npages;
 	new.flags = mem->flags;
@@ -812,9 +818,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	}
 #endif /* not defined CONFIG_S390 */
 
-	if (!npages)
-		kvm_arch_flush_shadow(kvm);
-
 	spin_lock(&kvm->mmu_lock);
 	if (mem->slot >= kvm->nmemslots)
 		kvm->nmemslots = mem->slot + 1;
-- 
1.5.6.5