migration/multifd: Allow clearing of the file_bmap from multifd

We currently only need to clear the mapped-ram file bitmap from the
migration thread during save_zero_page.

We're about to add support for zero page detection on the multifd
thread, so allow ramblock_set_file_bmap_atomic() to also clear the
bits.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240311180015.3359271-3-hao.xiang@linux.dev
Signed-off-by: Peter Xu <peterx@redhat.com>

migration/multifd.c

@@ -115,7 +115,7 @@ static void multifd_set_file_bitmap(MultiFDSendParams *p)
     assert(pages->block);
 
     for (int i = 0; i < p->pages->num; i++) {
-        ramblock_set_file_bmap_atomic(pages->block, pages->offset[i]);
+        ramblock_set_file_bmap_atomic(pages->block, pages->offset[i], true);
     }
 }
 

migration/ram.c

@@ -3149,9 +3149,13 @@ static void ram_save_file_bmap(QEMUFile *f)
     }
 }
 
-void ramblock_set_file_bmap_atomic(RAMBlock *block, ram_addr_t offset)
+void ramblock_set_file_bmap_atomic(RAMBlock *block, ram_addr_t offset, bool set)
 {
-    set_bit_atomic(offset >> TARGET_PAGE_BITS, block->file_bmap);
+    if (set) {
+        set_bit_atomic(offset >> TARGET_PAGE_BITS, block->file_bmap);
+    } else {
+        clear_bit_atomic(offset >> TARGET_PAGE_BITS, block->file_bmap);
+    }
 }
 
 /**

migration/ram.h

@@ -75,7 +75,8 @@ bool ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *rb, Error **errp);
 bool ramblock_page_is_discarded(RAMBlock *rb, ram_addr_t start);
 void postcopy_preempt_shutdown_file(MigrationState *s);
 void *postcopy_preempt_thread(void *opaque);
-void ramblock_set_file_bmap_atomic(RAMBlock *block, ram_addr_t offset);
+void ramblock_set_file_bmap_atomic(RAMBlock *block, ram_addr_t offset,
+                                   bool set);
 
 /* ram cache */
 int colo_init_ram_cache(void);