KVM: Optimize overlapping memslots check

Do a quick lookup for possibly overlapping gfns when creating or moving
a memslot instead of performing a linear scan of the whole memslot set.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: tweaked params to avoid churn in future cleanup]
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <a4795e5c2f624754e9c0aab023ebda1966feb3e1.1638817641.git.maciej.szmigiero@oracle.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 130eaf1..d27568b 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1815,6 +1815,19 @@ static int kvm_set_memslot(struct kvm *kvm,
        return 0;
 }
 
+static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
+                                     gfn_t start, gfn_t end)
+{
+       struct kvm_memslot_iter iter;
+
+       kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) {
+               if (iter.slot->id != id)
+                       return true;
+       }
+
+       return false;
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -1826,8 +1839,9 @@ static int kvm_set_memslot(struct kvm *kvm,
 int __kvm_set_memory_region(struct kvm *kvm,
                            const struct kvm_userspace_memory_region *mem)
 {
-       struct kvm_memory_slot *old, *tmp;
+       struct kvm_memory_slot *old;
        struct kvm_memory_slot new;
+       struct kvm_memslots *slots;
        enum kvm_mr_change change;
        int as_id, id;
        int r;
@@ -1856,11 +1870,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
        if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
                return -EINVAL;
 
+       slots = __kvm_memslots(kvm, as_id);
+
        /*
         * Note, the old memslot (and the pointer itself!) may be invalidated
         * and/or destroyed by kvm_set_memslot().
         */
-       old = id_to_memslot(__kvm_memslots(kvm, as_id), id);
+       old = id_to_memslot(slots, id);
 
        if (!mem->memory_size) {
                if (!old || !old->npages)
@@ -1909,18 +1925,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
                        return 0;
        }
 
-       if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
-               int bkt;
-
-               /* Check for overlaps */
-               kvm_for_each_memslot(tmp, bkt, __kvm_memslots(kvm, as_id)) {
-                       if (tmp->id == id)
-                               continue;
-                       if (!((new.base_gfn + new.npages <= tmp->base_gfn) ||
-                             (new.base_gfn >= tmp->base_gfn + tmp->npages)))
-                               return -EEXIST;
-               }
-       }
+       if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) &&
+           kvm_check_memslot_overlap(slots, id, new.base_gfn,
+                                     new.base_gfn + new.npages))
+               return -EEXIST;
 
        return kvm_set_memslot(kvm, old, &new, change);
 }