[v4,09/13] memory: Attach RamBlockAttribute to guest_memfd-backed RAMBlocks

Commit Message

Chenyi Qiang April 7, 2025, 7:49 a.m. UTC

A new field, ram_block_attribute, is introduced in RAMBlock to link to a
RamBlockAttribute object. This change centralizes all guest_memfd state
information (such as fd and shared_bitmap) within a RAMBlock,
simplifying management.

The realize()/unrealized() helpers are used to initialize/uninitialize
the RamBlockAttribute object. The object is registered/unregistered in
the target RAMBlock's MemoryRegion when creating guest_memfd.

Additionally, use the private_shared_manager_state_change() helper to
notify the registered PrivateSharedListener of these changes.

Signed-off-by: Chenyi Qiang <[e-mail]>
---
Changes in v4:
    - Remove the replay operations for attribute changes which will be
      handled in a listener in following patches.
    - Add some comment in the error path of realize() to remind the
      future development of the unified error path.

Changes in v3:
    - Use ram_discard_manager_reply_populated/discarded() to set the
      memory attribute and add the undo support if state_change()
      failed.
    - Didn't add Reviewed-by from Alexey due to the new changes in this
      commit.

Changes in v2:
    - Introduce a new field memory_attribute_manager in RAMBlock.
    - Move the state_change() handling during page conversion in this patch.
    - Undo what we did if it fails to set.
    - Change the order of close(guest_memfd) and memory_attribute_manager cleanup.
---
 accel/kvm/kvm-all.c     |  9 +++++++++
 include/exec/ramblock.h |  1 +
 system/physmem.c        | 16 ++++++++++++++++
 3 files changed, 26 insertions(+)

Patch

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index c1fea69d58..546b58b737 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -3088,6 +3088,15 @@  int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
     addr = memory_region_get_ram_ptr(mr) + section.offset_within_region;
     rb = qemu_ram_block_from_host(addr, false, &offset);
 
+    ret = private_shared_manager_state_change(PRIVATE_SHARED_MANAGER(mr->gsm),
+                                              offset, size, to_private);
+    if (ret) {
+        error_report("Failed to notify the listener the state change of "
+                     "(0x%"HWADDR_PRIx" + 0x%"HWADDR_PRIx") to %s",
+                     start, size, to_private ? "private" : "shared");
+        goto out_unref;
+    }
+
     if (to_private) {
         if (rb->page_size != qemu_real_host_page_size()) {
             /*
diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h
index b8b5469db9..78eb031819 100644
--- a/include/exec/ramblock.h
+++ b/include/exec/ramblock.h
@@ -46,6 +46,7 @@  struct RAMBlock {
     int fd;
     uint64_t fd_offset;
     int guest_memfd;
+    RamBlockAttribute *ram_block_attribute;
     size_t page_size;
     /* dirty bitmap used during migration */
     unsigned long *bmap;
diff --git a/system/physmem.c b/system/physmem.c
index c76503aea8..fb74321e10 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -1885,6 +1885,20 @@  static void ram_block_add(RAMBlock *new_block, Error **errp)
             qemu_mutex_unlock_ramlist();
             goto out_free;
         }
+
+        new_block->ram_block_attribute = RAM_BLOCK_ATTRIBUTE(object_new(TYPE_RAM_BLOCK_ATTRIBUTE));
+        if (ram_block_attribute_realize(new_block->ram_block_attribute, new_block->mr)) {
+            error_setg(errp, "Failed to realize ram block attribute");
+            /*
+             * The error path could be unified if the rest of ram_block_add() ever
+             * develops a need to check for errors.
+             */
+            object_unref(OBJECT(new_block->ram_block_attribute));
+            close(new_block->guest_memfd);
+            ram_block_discard_require(false);
+            qemu_mutex_unlock_ramlist();
+            goto out_free;
+        }
     }
 
     ram_size = (new_block->offset + new_block->max_length) >> TARGET_PAGE_BITS;
@@ -2138,6 +2152,8 @@  static void reclaim_ramblock(RAMBlock *block)
     }
 
     if (block->guest_memfd >= 0) {
+        ram_block_attribute_unrealize(block->ram_block_attribute);
+        object_unref(OBJECT(block->ram_block_attribute));
         close(block->guest_memfd);
         ram_block_discard_require(false);
     }