accel: kvm: Add aligment assert for kvm_log_clear_one_slot

The parameters start and size are transfered from QEMU memory
emulation layer. It can promise that they are TARGET_PAGE_SIZE
aligned. However, KVM needs they are qemu_real_page_size aligned.

Though no caller breaks this aligned requirement currently, we'd
better add an explicit assert to avoid future breaking.

Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Message-Id: <20201217014941.22872-3-zhukeqian1@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/kvm/kvm-all.c

@@ -673,6 +673,10 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
 #define KVM_CLEAR_LOG_ALIGN  (qemu_real_host_page_size << KVM_CLEAR_LOG_SHIFT)
 #define KVM_CLEAR_LOG_MASK   (-KVM_CLEAR_LOG_ALIGN)
 
+/*
+ * As the granule of kvm dirty log is qemu_real_host_page_size,
+ * @start and @size are expected and restricted to align to it.
+ */
 static int kvm_log_clear_one_slot(KVMSlot *mem, int as_id, uint64_t start,
                                   uint64_t size)
 {
@@ -682,6 +686,9 @@ static int kvm_log_clear_one_slot(KVMSlot *mem, int as_id, uint64_t start,
     unsigned long *bmap_clear = NULL, psize = qemu_real_host_page_size;
     int ret;
 
+    /* Make sure start and size are qemu_real_host_page_size aligned */
+    assert(QEMU_IS_ALIGNED(start | size, psize));
+
     /*
      * We need to extend either the start or the size or both to
      * satisfy the KVM interface requirement.  Firstly, do the start