[PULL 13/20] KVM: Create the KVMSlot dirty bitmap on flag changes

[Paolo Bonzini <pbonzini@redhat.com>]

From: Peter Xu <peterx@redhat.com>

Previously we have two places that will create the per KVMSlot dirty
bitmap:

  1. When a newly created KVMSlot has dirty logging enabled,
  2. When the first log_sync() happens for a memory slot.

The 2nd case is lazy-init, while the 1st case is not (which is a fix
of what the 2nd case missed).

To do explicit initialization of dirty bitmaps, what we're missing is
to create the dirty bitmap when the slot changed from not-dirty-track
to dirty-track.  Do that in kvm_slot_update_flags().

With that, we can safely remove the 2nd lazy-init.

This change will be needed for kvm dirty ring because kvm dirty ring
does not use the log_sync() interface at all.

Also move all the pre-checks into kvm_slot_init_dirty_bitmap().

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210506160549.130416-4-peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 accel/kvm/kvm-all.c | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index f8980e155b..5bc40fd71b 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -177,6 +177,8 @@ static QemuMutex kml_slots_lock;
 #define kvm_slots_lock()    qemu_mutex_lock(&kml_slots_lock)
 #define kvm_slots_unlock()  qemu_mutex_unlock(&kml_slots_lock)
 
+static void kvm_slot_init_dirty_bitmap(KVMSlot *mem);
+
 static inline void kvm_resample_fd_remove(int gsi)
 {
     KVMResampleFd *rfd;
@@ -500,6 +502,7 @@ static int kvm_slot_update_flags(KVMMemoryListener *kml, KVMSlot *mem,
         return 0;
     }
 
+    kvm_slot_init_dirty_bitmap(mem);
     return kvm_set_user_memory_region(kml, mem, false);
 }
 
@@ -584,8 +587,12 @@ static int kvm_get_dirty_pages_log_range(MemoryRegionSection *section,
 #define ALIGN(x, y)  (((x)+(y)-1) & ~((y)-1))
 
 /* Allocate the dirty bitmap for a slot  */
-static void kvm_memslot_init_dirty_bitmap(KVMSlot *mem)
+static void kvm_slot_init_dirty_bitmap(KVMSlot *mem)
 {
+    if (!(mem->flags & KVM_MEM_LOG_DIRTY_PAGES) || mem->dirty_bmap) {
+        return;
+    }
+
     /*
      * XXX bad kernel interface alert
      * For dirty bitmap, kernel allocates array of size aligned to
@@ -640,11 +647,6 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
             goto out;
         }
 
-        if (!mem->dirty_bmap) {
-            /* Allocate on the first log_sync, once and for all */
-            kvm_memslot_init_dirty_bitmap(mem);
-        }
-
         d.dirty_bitmap = mem->dirty_bmap;
         d.slot = mem->slot | (kml->as_id << 16);
         ret = kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d);
@@ -1181,14 +1183,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
         mem->start_addr = start_addr;
         mem->ram = ram;
         mem->flags = kvm_mem_flags(mr);
-
-        if (mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
-            /*
-             * Reallocate the bmap; it means it doesn't disappear in
-             * middle of a migrate.
-             */
-            kvm_memslot_init_dirty_bitmap(mem);
-        }
+        kvm_slot_init_dirty_bitmap(mem);
         err = kvm_set_user_memory_region(kml, mem, true);
         if (err) {
             fprintf(stderr, "%s: error registering slot: %s\n", __func__,
-- 
2.27.0