[PATCH v5 07/65] physmem: Introduce ram_block_discard_guest_memfd_range()

[Xiaoyao Li <xiaoyao.li@xxxxxxxxx>]

When memory page is converted from private to shared, the original
private memory is back'ed by guest_memfd. Introduce
ram_block_discard_guest_memfd_range() for discarding memory in
guest_memfd.

Originally-from: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Codeveloped-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
---
Changes in v5:
- Collect Reviewed-by from David;

Changes in in v4:
- Drop ram_block_convert_range() and open code its implementation in the
  next Patch.
---
 include/exec/cpu-common.h |  2 ++
 system/physmem.c          | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 9ead1be10057..ccd46ad3e173 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -166,6 +166,8 @@ typedef int (RAMBlockIterFunc)(RAMBlock *rb, void *opaque);
 
 int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque);
 int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length);
+int ram_block_discard_guest_memfd_range(RAMBlock *rb, uint64_t start,
+                                        size_t length);
 
 #endif
 
diff --git a/system/physmem.c b/system/physmem.c
index c4fc1e506de8..8c9368bc99ef 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -3618,6 +3618,29 @@ err:
     return ret;
 }
 
+int ram_block_discard_guest_memfd_range(RAMBlock *rb, uint64_t start,
+                                        size_t length)
+{
+    int ret = -1;
+
+#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+    ret = fallocate(rb->guest_memfd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+                    start, length);
+
+    if (ret) {
+        ret = -errno;
+        error_report("%s: Failed to fallocate %s:%" PRIx64 " +%zx (%d)",
+                     __func__, rb->idstr, start, length, ret);
+    }
+#else
+    ret = -ENOSYS;
+    error_report("%s: fallocate not available %s:%" PRIx64 " +%zx (%d)",
+                 __func__, rb->idstr, start, length, ret);
+#endif
+
+    return ret;
+}
+
 bool ramblock_is_pmem(RAMBlock *rb)
 {
     return rb->flags & RAM_PMEM;
-- 
2.34.1