Allocate anonymous memory using mmap MAP_ANON or memfd_create depending
on the value of the anon-alloc machine property. This option applies to
memory allocated as a side effect of creating various devices. It does
not apply to memory-backend-objects, whether explicitly specified on
the command line, or implicitly created by the -m command line option.
The memfd option is intended to support new migration modes, in which the
memory region can be transferred in place to a new QEMU process, by sending
the memfd file descriptor to the process. Memory contents are preserved,
and if the mode also transfers device descriptors, then pages that are
locked in memory for DMA remain locked. This behavior is a pre-requisite
for supporting vfio, vdpa, and iommufd devices with the new modes.
Signed-off-by: Steve Sistare <steven.sist...@oracle.com>
---
hw/core/machine.c | 19 +++++++++++++++++++
include/hw/boards.h | 1 +
qapi/machine.json | 14 ++++++++++++++
qemu-options.hx | 11 +++++++++++
system/physmem.c | 35 +++++++++++++++++++++++++++++++++++
system/trace-events | 3 +++
6 files changed, 83 insertions(+)
diff --git a/hw/core/machine.c b/hw/core/machine.c
index adaba17..a89a32b 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -460,6 +460,20 @@ static void machine_set_mem_merge(Object *obj, bool value,
Error **errp)
ms->mem_merge = value;
}
+static int machine_get_anon_alloc(Object *obj, Error **errp)
+{
+ MachineState *ms = MACHINE(obj);
+
+ return ms->anon_alloc;
+}
+
+static void machine_set_anon_alloc(Object *obj, int value, Error **errp)
+{
+ MachineState *ms = MACHINE(obj);
+
+ ms->anon_alloc = value;
+}
+
static bool machine_get_usb(Object *obj, Error **errp)
{
MachineState *ms = MACHINE(obj);
@@ -1078,6 +1092,11 @@ static void machine_class_init(ObjectClass *oc, void
*data)
object_class_property_set_description(oc, "mem-merge",
"Enable/disable memory merge support");
+ object_class_property_add_enum(oc, "anon-alloc", "AnonAllocOption",
+ &AnonAllocOption_lookup,
+ machine_get_anon_alloc,
+ machine_set_anon_alloc);
+
object_class_property_add_bool(oc, "usb",
machine_get_usb, machine_set_usb);
object_class_property_set_description(oc, "usb",
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 5966069..5a87647 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -393,6 +393,7 @@ struct MachineState {
bool enable_graphics;
ConfidentialGuestSupport *cgs;
HostMemoryBackend *memdev;
+ AnonAllocOption anon_alloc;
/*
* convenience alias to ram_memdev_id backend memory region
* or to numa container memory region
diff --git a/qapi/machine.json b/qapi/machine.json
index a6b8795..d4a63f5 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1898,3 +1898,17 @@
{ 'command': 'x-query-interrupt-controllers',
'returns': 'HumanReadableText',
'features': [ 'unstable' ]}
+
+##
+# @AnonAllocOption:
+#
+# An enumeration of the options for allocating anonymous guest memory.
+#
+# @mmap: allocate using mmap MAP_ANON
+#
+# @memfd: allocate using memfd_create
+#
+# Since: 9.2
+##
+{ 'enum': 'AnonAllocOption',
+ 'data': [ 'mmap', 'memfd' ] }
diff --git a/qemu-options.hx b/qemu-options.hx
index d94e2cb..90ab943 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -38,6 +38,7 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
" nvdimm=on|off controls NVDIMM support (default=off)\n"
" memory-encryption=@var{} memory encryption object to use
(default=none)\n"
" hmat=on|off controls ACPI HMAT support (default=off)\n"
+ " anon-alloc=mmap|memfd allocate anonymous guest RAM using mmap
MAP_ANON or memfd_create (default: mmap)\n"
" memory-backend='backend-id' specifies explicitly provided
backend for main RAM (default=none)\n"
"
cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n",
QEMU_ARCH_ALL)
@@ -101,6 +102,16 @@ SRST
Enables or disables ACPI Heterogeneous Memory Attribute Table
(HMAT) support. The default is off.
+ ``anon-alloc=mmap|memfd``
+ Allocate anonymous guest RAM using mmap MAP_ANON (the default)
+ or memfd_create. This option applies to memory allocated as a
+ side effect of creating various devices. It does not apply to
+ memory-backend-objects, whether explicitly specified on the
+ command line, or implicitly created by the -m command line
+ option.
+
+ Some migration modes require anon-alloc=memfd.
+
``memory-backend='id'``
An alternative to legacy ``-mem-path`` and ``mem-prealloc`` options.
Allows to use a memory backend as main RAM.
diff --git a/system/physmem.c b/system/physmem.c
index dc1db3a..174f7e0 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -47,6 +47,7 @@
#include "qemu/qemu-print.h"
#include "qemu/log.h"
#include "qemu/memalign.h"
+#include "qemu/memfd.h"
#include "exec/memory.h"
#include "exec/ioport.h"
#include "sysemu/dma.h"
@@ -69,6 +70,8 @@
#include "qemu/pmem.h"
+#include "qapi/qapi-types-migration.h"
+#include "migration/options.h"
#include "migration/vmstate.h"
#include "qemu/range.h"
@@ -1849,6 +1852,35 @@ static void ram_block_add(RAMBlock *new_block, Error
**errp)
qemu_mutex_unlock_ramlist();
return;
}
+
+ } else if (current_machine->anon_alloc == ANON_ALLOC_OPTION_MEMFD &&
+ !object_dynamic_cast(new_block->mr->parent_obj.parent,
+ TYPE_MEMORY_BACKEND)) {
