KVM: Don't make a full copy of the old memslot in __kvm_set_memory_region()

Stop making a full copy of the old memslot in __kvm_set_memory_region()
now that metadata updates are handled by kvm_set_memslot(), i.e. now that
the old memslot's dirty bitmap doesn't need to be referenced after the
memslot and its pointer is modified/invalidated by kvm_set_memslot().

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <5dce0946b41bba8c83f6e3424c6955c56bcc9f86.1638817640.git.maciej.szmigiero@oracle.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ec5567e8442b97ccf3cee93d9a8c9c5b7bac7a65..8ccb1ac82d38e8d679a5564dcfbdf7d820c9ae2d 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1730,8 +1730,8 @@ out_slots:
 int __kvm_set_memory_region(struct kvm *kvm,
                            const struct kvm_userspace_memory_region *mem)
 {
-       struct kvm_memory_slot old, new;
-       struct kvm_memory_slot *tmp;
+       struct kvm_memory_slot *old, *tmp;
+       struct kvm_memory_slot new;
        enum kvm_mr_change change;
        int as_id, id;
        int r;
@@ -1761,25 +1761,16 @@ int __kvm_set_memory_region(struct kvm *kvm,
                return -EINVAL;
 
        /*
-        * Make a full copy of the old memslot, the pointer will become stale
-        * when the memslots are re-sorted by update_memslots(), and the old
-        * memslot needs to be referenced after calling update_memslots(), e.g.
-        * to free its resources and for arch specific behavior.
+        * Note, the old memslot (and the pointer itself!) may be invalidated
+        * and/or destroyed by kvm_set_memslot().
         */
-       tmp = id_to_memslot(__kvm_memslots(kvm, as_id), id);
-       if (tmp) {
-               old = *tmp;
-               tmp = NULL;
-       } else {
-               memset(&old, 0, sizeof(old));
-               old.id = id;
-       }
+       old = id_to_memslot(__kvm_memslots(kvm, as_id), id);
 
        if (!mem->memory_size) {
-               if (!old.npages)
+               if (!old || !old->npages)
                        return -EINVAL;
 
-               if (WARN_ON_ONCE(kvm->nr_memslot_pages < old.npages))
+               if (WARN_ON_ONCE(kvm->nr_memslot_pages < old->npages))
                        return -EIO;
 
                memset(&new, 0, sizeof(new));
@@ -1799,7 +1790,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
        if (new.npages > KVM_MEM_MAX_NR_PAGES)
                return -EINVAL;
 
-       if (!old.npages) {
+       if (!old || !old->npages) {
                change = KVM_MR_CREATE;
 
                /*
@@ -1809,14 +1800,14 @@ int __kvm_set_memory_region(struct kvm *kvm,
                if ((kvm->nr_memslot_pages + new.npages) < kvm->nr_memslot_pages)
                        return -EINVAL;
        } else { /* Modify an existing slot. */
-               if ((new.userspace_addr != old.userspace_addr) ||
-                   (new.npages != old.npages) ||
-                   ((new.flags ^ old.flags) & KVM_MEM_READONLY))
+               if ((new.userspace_addr != old->userspace_addr) ||
+                   (new.npages != old->npages) ||
+                   ((new.flags ^ old->flags) & KVM_MEM_READONLY))
                        return -EINVAL;
 
-               if (new.base_gfn != old.base_gfn)
+               if (new.base_gfn != old->base_gfn)
                        change = KVM_MR_MOVE;
-               else if (new.flags != old.flags)
+               else if (new.flags != old->flags)
                        change = KVM_MR_FLAGS_ONLY;
                else /* Nothing to change. */
                        return 0;