KVM: Provide helper to get kvm dirty log

Provide a helper kvm_slot_get_dirty_log() to make the function
kvm_physical_sync_dirty_bitmap() clearer.  We can even cache the as_id
into KVMSlot when it is created, so that we don't even need to pass it
down every time.

Since at it, remove return value of kvm_physical_sync_dirty_bitmap()
because it should never fail.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210506160549.130416-5-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

accel/kvm/kvm-all.c

@@ -615,6 +615,30 @@ static void kvm_slot_init_dirty_bitmap(KVMSlot *mem)
     mem->dirty_bmap = g_malloc0(bitmap_size);
 }
 
+/*
+ * Sync dirty bitmap from kernel to KVMSlot.dirty_bmap, return true if
+ * succeeded, false otherwise
+ */
+static bool kvm_slot_get_dirty_log(KVMState *s, KVMSlot *slot)
+{
+    struct kvm_dirty_log d = {};
+    int ret;
+
+    d.dirty_bitmap = slot->dirty_bmap;
+    d.slot = slot->slot | (slot->as_id << 16);
+    ret = kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d);
+
+    if (ret == -ENOENT) {
+        /* kernel does not have dirty bitmap in this slot */
+        ret = 0;
+    }
+    if (ret) {
+        error_report_once("%s: KVM_GET_DIRTY_LOG failed with %d",
+                          __func__, ret);
+    }
+    return ret == 0;
+}
+
 /**
  * kvm_physical_sync_dirty_bitmap - Sync dirty bitmap from kernel space
  *
@@ -626,15 +650,13 @@ static void kvm_slot_init_dirty_bitmap(KVMSlot *mem)
  * @kml: the KVM memory listener object
  * @section: the memory section to sync the dirty bitmap with
  */
-static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
+static void kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
-                                          MemoryRegionSection *section)
+                                           MemoryRegionSection *section)
 {
     KVMState *s = kvm_state;
-    struct kvm_dirty_log d = {};
     KVMSlot *mem;
     hwaddr start_addr, size;
     hwaddr slot_size, slot_offset = 0;
-    int ret = 0;
 
     size = kvm_align_section(section, &start_addr);
     while (size) {
@@ -644,19 +666,10 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
         mem = kvm_lookup_matching_slot(kml, start_addr, slot_size);
         if (!mem) {
             /* We don't have a slot if we want to trap every access. */
-            goto out;
+            return;
         }
 
-        d.dirty_bitmap = mem->dirty_bmap;
+        if (kvm_slot_get_dirty_log(s, mem)) {
-        d.slot = mem->slot | (kml->as_id << 16);
-        ret = kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d);
-        if (ret == -ENOENT) {
-            /* kernel does not have dirty bitmap in this slot */
-            ret = 0;
-        } else if (ret < 0) {
-            error_report("ioctl KVM_GET_DIRTY_LOG failed: %d", errno);
-            goto out;
-        } else {
             subsection.offset_within_region += slot_offset;
             subsection.size = int128_make64(slot_size);
             kvm_get_dirty_pages_log_range(&subsection, d.dirty_bitmap);
@@ -666,8 +679,6 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
         start_addr += slot_size;
         size -= slot_size;
     }
-out:
-    return ret;
 }
 
 /* Alignment requirement for KVM_CLEAR_DIRTY_LOG - 64 pages */
@@ -1179,6 +1190,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
     do {
         slot_size = MIN(kvm_max_slot_size, size);
         mem = kvm_alloc_slot(kml);
+        mem->as_id = kml->as_id;
         mem->memory_size = slot_size;
         mem->start_addr = start_addr;
         mem->ram = ram;
@@ -1221,14 +1233,10 @@ static void kvm_log_sync(MemoryListener *listener,
                          MemoryRegionSection *section)
 {
     KVMMemoryListener *kml = container_of(listener, KVMMemoryListener, listener);
-    int r;
 
     kvm_slots_lock();
-    r = kvm_physical_sync_dirty_bitmap(kml, section);
+    kvm_physical_sync_dirty_bitmap(kml, section);
     kvm_slots_unlock();
-    if (r < 0) {
-        abort();
-    }
 }
 
 static void kvm_log_clear(MemoryListener *listener,

include/sysemu/kvm_int.h

@@ -23,6 +23,8 @@ typedef struct KVMSlot
     int old_flags;
     /* Dirty bitmap cache for the slot */
     unsigned long *dirty_bmap;
+    /* Cache of the address space ID */
+    int as_id;
 } KVMSlot;
 
 typedef struct KVMMemoryListener {