hostmem: fix strict bind policy

When option -mem-prealloc is used with one or more memory-backend
objects, created backends may not obey configured bind policy or
creation may fail after kernel attempts to move pages according
to bind policy.
Reason is in file_ram_alloc(), which will pre-allocate
any descriptor based RAM if global mem_prealloc != 0 and that
happens way before bind policy is applied to memory range.

One way to fix it would be to extend memory_region_foo() API
and add more invariants that could broken later due implicit
dependencies that's hard to track.

Another approach is to drop adhoc main RAM allocation and
consolidate it around memory-backend. That allows to have
single place that allocates guest RAM (main and memdev)
in the same way and then global mem_prealloc could be
replaced by backend's property[s] that will affect created
memory-backend objects but only in correct order this time.

With main RAM now converted to hostmem backends, there is no
point in keeping global mem_prealloc around, so alias
 -mem-prealloc to "memory-backend.prealloc=on"
machine compat[*] property and make mem_prealloc a local
variable to only stir registration of compat property.

*) currently user accessible -global works only with DEVICE
   based objects and extra work is needed to make it work
   with hostmem backends. But that is convenience option
   and out of scope of this already huge refactoring.
   Hence machine compat properties were used.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20200219160953.13771-78-imammedo@redhat.com>

backends/hostmem-file.c

@@ -51,7 +51,6 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         return;
     }
 
-    backend->force_prealloc = mem_prealloc;
     name = host_memory_backend_get_name(backend);
     memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
                                      name,

backends/hostmem-memfd.c

@@ -45,7 +45,6 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         return;
     }
 
-    backend->force_prealloc = mem_prealloc;
     fd = qemu_memfd_create(TYPE_MEMORY_BACKEND_MEMFD, backend->size,
                            m->hugetlb, m->hugetlbsize, m->seal ?
                            F_SEAL_GROW | F_SEAL_SHRINK | F_SEAL_SEAL : 0,

backends/hostmem.c

@@ -215,7 +215,7 @@ static bool host_memory_backend_get_prealloc(Object *obj, Error **errp)
 {
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
 
-    return backend->prealloc || backend->force_prealloc;
+    return backend->prealloc;
 }
 
 static void host_memory_backend_set_prealloc(Object *obj, bool value,
@@ -224,14 +224,6 @@ static void host_memory_backend_set_prealloc(Object *obj, bool value,
     Error *local_err = NULL;
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
 
-    if (backend->force_prealloc) {
-        if (value) {
-            error_setg(errp,
-                       "remove -mem-prealloc to use the prealloc property");
-            return;
-        }
-    }
-
     if (!host_memory_backend_mr_inited(backend)) {
         backend->prealloc = value;
         return;
@@ -288,8 +280,6 @@ static void host_memory_backend_init(Object *obj)
     /* TODO: convert access to globals to compat properties */
     backend->merge = machine_mem_merge(machine);
     backend->dump = machine_dump_guest_core(machine);
-    backend->prealloc = mem_prealloc;
-    backend->prealloc_threads = 1;
 }
 
 static void host_memory_backend_post_init(Object *obj)

exec.c

@@ -1801,8 +1801,6 @@ static void *file_ram_alloc(RAMBlock *block,
                             bool truncate,
                             Error **errp)
 {
-    Error *err = NULL;
-    MachineState *ms = MACHINE(qdev_get_machine());
     void *area;
 
     block->page_size = qemu_fd_getpagesize(fd);
@@ -1858,15 +1856,6 @@ static void *file_ram_alloc(RAMBlock *block,
         return NULL;
     }
 
-    if (mem_prealloc) {
-        os_mem_prealloc(fd, area, memory, ms->smp.cpus, &err);
-        if (err) {
-            error_propagate(errp, err);
-            qemu_ram_munmap(fd, area, memory);
-            return NULL;
-        }
-    }
-
     block->fd = fd;
     return area;
 }

include/sysemu/hostmem.h

@@ -70,7 +70,7 @@ struct HostMemoryBackend {
     /* protected */
     uint64_t size;
     bool merge, dump, use_canonical_path;
-    bool prealloc, force_prealloc, is_mapped, share;
+    bool prealloc, is_mapped, share;
     uint32_t prealloc_threads;
     DECLARE_BITMAP(host_nodes, MAX_NODES + 1);
     HostMemPolicy policy;

include/sysemu/sysemu.h

@@ -50,7 +50,6 @@ extern uint8_t *boot_splash_filedata;
 extern bool enable_mlock;
 extern bool enable_cpu_pm;
 extern QEMUClockType rtc_clock;
-extern int mem_prealloc;
 
 #define MAX_OPTION_ROMS 16
 typedef struct QEMUOptionRom {

vl.c

@@ -140,7 +140,6 @@ enum vga_retrace_method vga_retrace_method = VGA_RETRACE_DUMB;
 int display_opengl;
 const char* keyboard_layout = NULL;
 ram_addr_t ram_size;
-int mem_prealloc = 0; /* force preallocation of physical target memory */
 bool enable_mlock = false;
 bool enable_cpu_pm = false;
 int nb_nics;
@@ -2883,6 +2882,7 @@ int main(int argc, char **argv, char **envp)
     const char *mem_path = NULL;
     BlockdevOptionsQueue bdo_queue = QSIMPLEQ_HEAD_INITIALIZER(bdo_queue);
     QemuPluginList plugin_list = QTAILQ_HEAD_INITIALIZER(plugin_list);
+    int mem_prealloc = 0; /* force preallocation of physical target memory */
 
     os_set_line_buffering();
 
@@ -3984,6 +3984,7 @@ int main(int argc, char **argv, char **envp)
         val = g_strdup_printf("%d", current_machine->smp.cpus);
         object_register_sugar_prop("memory-backend", "prealloc-threads", val);
         g_free(val);
+        object_register_sugar_prop("memory-backend", "prealloc", "on");
     }
 
     /*