kvm: clear dirty bitmaps from all overlapping memslots

Currently MemoryRegionSection has 1:1 mapping to KVMSlot.
However next patch will allow splitting MemoryRegionSection into
several KVMSlot-s, make sure that kvm_physical_log_slot_clear()
is able to handle such 1:N mapping.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Reviewed-by: NPeter Xu <peterx@redhat.com>
Message-Id: <20190924144751.24149-3-imammedo@redhat.com>
Acked-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NChristian Borntraeger <borntraeger@de.ibm.com>

accel/kvm/kvm-all.c

@@ -589,8 +589,8 @@ static int kvm_log_clear_one_slot(KVMSlot *mem, int as_id, uint64_t start,
      * satisfy the KVM interface requirement.  Firstly, do the start
      * page alignment on 64 host pages
      */
-    bmap_start = (start - mem->start_addr) & KVM_CLEAR_LOG_MASK;
-    start_delta = start - mem->start_addr - bmap_start;
+    bmap_start = start & KVM_CLEAR_LOG_MASK;
+    start_delta = start - bmap_start;
     bmap_start /= psize;
 
     /*
@@ -694,8 +694,8 @@ static int kvm_physical_log_clear(KVMMemoryListener *kml,
                                   MemoryRegionSection *section)
 {
     KVMState *s = kvm_state;
-    uint64_t start, size;
-    KVMSlot *mem = NULL;
+    uint64_t start, size, offset, count;
+    KVMSlot *mem;
     int ret, i;
 
     if (!s->manual_dirty_log_protect) {
@@ -713,22 +713,30 @@ static int kvm_physical_log_clear(KVMMemoryListener *kml,
 
     kvm_slots_lock(kml);
 
-    /* Find any possible slot that covers the section */
     for (i = 0; i < s->nr_slots; i++) {
         mem = &kml->slots[i];
-        if (mem->start_addr <= start &&
-            start + size <= mem->start_addr + mem->memory_size) {
+        /* Discard slots that are empty or do not overlap the section */
+        if (!mem->memory_size ||
+            mem->start_addr > start + size - 1 ||
+            start > mem->start_addr + mem->memory_size - 1) {
+            continue;
+        }
+
+        if (start >= mem->start_addr) {
+            /* The slot starts before section or is aligned to it.  */
+            offset = start - mem->start_addr;
+            count = MIN(mem->memory_size - offset, size);
+        } else {
+            /* The slot starts after section.  */
+            offset = 0;
+            count = MIN(mem->memory_size, size - (mem->start_addr - start));
+        }
+        ret = kvm_log_clear_one_slot(mem, kml->as_id, offset, count);
+        if (ret < 0) {
             break;
         }
     }
 
-    /*
-     * We should always find one memslot until this point, otherwise
-     * there could be something wrong from the upper layer
-     */
-    assert(mem && i != s->nr_slots);
-    ret = kvm_log_clear_one_slot(mem, kml->as_id, start, size);
-
     kvm_slots_unlock(kml);
 
     return ret;