Support the guest-memfd type when the fd has init share enabled.  It means
the gmemfd can be used similarly to memfd.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 tests/qtest/migration/framework.h |  4 +++
 tests/qtest/migration/framework.c | 60 +++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/tests/qtest/migration/framework.h b/tests/qtest/migration/framework.h
index ed85ed502d..b4c5edcad3 100644
--- a/tests/qtest/migration/framework.h
+++ b/tests/qtest/migration/framework.h
@@ -34,6 +34,10 @@ typedef enum {
      * but only anonymously allocated.
      */
     MEM_TYPE_MEMFD,
+    /*
+     * Use guest-memfd, shared mappings.
+     */
+    MEM_TYPE_GUEST_MEMFD,
     MEM_TYPE_NUM,
 } MemType;
 
diff --git a/tests/qtest/migration/framework.c b/tests/qtest/migration/framework.c
index 81eae09c92..73536c8f29 100644
--- a/tests/qtest/migration/framework.c
+++ b/tests/qtest/migration/framework.c
@@ -26,6 +26,10 @@
 #include "qemu/range.h"
 #include "qemu/sockets.h"
 
+#ifdef CONFIG_LINUX
+#include <linux/kvm.h>
+#include <sys/ioctl.h>
+#endif
 
 #define QEMU_VM_FILE_MAGIC 0x5145564d
 #define QEMU_ENV_SRC "QTEST_QEMU_BINARY_SRC"
@@ -279,6 +283,9 @@ static char *migrate_mem_type_get_opts(MemType type, const char *memory_size)
     case MEM_TYPE_MEMFD:
         backend = g_strdup("-object memory-backend-memfd");
         break;
+    case MEM_TYPE_GUEST_MEMFD:
+        backend = g_strdup("-object memory-backend-memfd,guest-memfd=on");
+        break;
     case MEM_TYPE_ANON:
         backend = g_strdup("-object memory-backend-ram");
         share = false;
@@ -425,8 +432,55 @@ int migrate_args(char **from, char **to, const char *uri, MigrateStart *args)
     return 0;
 }
 
+static bool kvm_guest_memfd_init_shared_supported(const char **reason)
+{
+    assert(*reason == NULL);
+
+#ifdef CONFIG_LINUX
+    int ret, fd = -1;
+
+    if (!migration_get_env()->has_kvm) {
+        *reason = "KVM is not enabled in the current QEMU build";
+        goto out;
+    }
+
+    fd = open("/dev/kvm", O_RDWR);
+    if (fd < 0) {
+        *reason = "KVM module isn't available or missing permission";
+        goto out;
+    }
+
+    ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_GUEST_MEMFD);
+    if (!ret) {
+        *reason = "KVM module doesn't suport guest-memfd";
+        goto out;
+    }
+
+    ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_GUEST_MEMFD_FLAGS);
+    if (ret < 0) {
+        *reason = "KVM doesn't support KVM_CAP_GUEST_MEMFD_FLAGS";
+        goto out;
+    }
+
+    if (!(ret & GUEST_MEMFD_FLAG_INIT_SHARED)) {
+        *reason = "KVM doesn't support GUEST_MEMFD_FLAG_INIT_SHARED";
+        goto out;
+    }
+out:
+    if (fd >= 0) {
+        close(fd);
+    }
+#else
+    *reason = "KVM not supported on non-Linux OS";
+#endif
+
+    return !*reason;
+}
+
 static bool migrate_mem_type_prepare(MemType type)
 {
+    const char *reason = NULL;
+
     switch (type) {
     case MEM_TYPE_SHMEM:
         if (!g_file_test("/dev/shm", G_FILE_TEST_IS_DIR)) {
@@ -434,6 +488,12 @@ static bool migrate_mem_type_prepare(MemType type)
             return false;
         }
         break;
+    case MEM_TYPE_GUEST_MEMFD:
+        if (!kvm_guest_memfd_init_shared_supported(&reason)) {
+            g_test_skip(reason);
+            return false;
+        }
+        break;
     default:
         break;
     }
-- 
2.50.1