KVM: cleanup and add shortcuts to kvm_range_has_memory_attributes()

Use a guard to simplify early returns, and add two more easy
shortcuts.  If the requested attributes are invalid, the attributes
xarray will never show them as set.  And if testing a single page,
kvm_get_memory_attributes() is more efficient.

Reviewed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d0788d0a72cc090c8d4eef33c9b05a9d0a923a43..30328ff2d8407c7e14776e3b4ffa8b9d1505db93 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2398,6 +2398,14 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
 #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */
 
 #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
+static u64 kvm_supported_mem_attributes(struct kvm *kvm)
+{
+       if (!kvm || kvm_arch_has_private_mem(kvm))
+               return KVM_MEMORY_ATTRIBUTE_PRIVATE;
+
+       return 0;
+}
+
 /*
  * Returns true if _all_ gfns in the range [@start, @end) have attributes
  * matching @attrs.
@@ -2406,40 +2414,30 @@ bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
                                     unsigned long attrs)
 {
        XA_STATE(xas, &kvm->mem_attr_array, start);
+       unsigned long mask = kvm_supported_mem_attributes(kvm);
        unsigned long index;
-       bool has_attrs;
        void *entry;
 
-       rcu_read_lock();
+       if (attrs & ~mask)
+               return false;
 
-       if (!attrs) {
-               has_attrs = !xas_find(&xas, end - 1);
-               goto out;
-       }
+       if (end == start + 1)
+               return kvm_get_memory_attributes(kvm, start) == attrs;
+
+       guard(rcu)();
+       if (!attrs)
+               return !xas_find(&xas, end - 1);
 
-       has_attrs = true;
        for (index = start; index < end; index++) {
                do {
                        entry = xas_next(&xas);
                } while (xas_retry(&xas, entry));
 
-               if (xas.xa_index != index || xa_to_value(entry) != attrs) {
-                       has_attrs = false;
-                       break;
-               }
+               if (xas.xa_index != index || xa_to_value(entry) != attrs)
+                       return false;
        }
 
-out:
-       rcu_read_unlock();
-       return has_attrs;
-}
-
-static u64 kvm_supported_mem_attributes(struct kvm *kvm)
-{
-       if (!kvm || kvm_arch_has_private_mem(kvm))
-               return KVM_MEMORY_ATTRIBUTE_PRIVATE;
-
-       return 0;
+       return true;
 }
 
 static __always_inline void kvm_handle_gfn_range(struct kvm *kvm,