Re: [PATCH V7 10/29] machine: memfd-alloc option

[Steven Sistare]

On 2/18/2022 3:05 AM, Guoyi Tu wrote:
> On Wed, 2021-12-22 at 11:05 -0800, Steve Sistare wrote:
>> Allocate anonymous memory using memfd_create if the memfd-alloc
>> machine
>> option is set.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>  hw/core/machine.c   | 19 +++++++++++++++++++
>>  include/hw/boards.h |  1 +
>>  qemu-options.hx     |  6 ++++++
>>  softmmu/physmem.c   | 47 ++++++++++++++++++++++++++++++++++++++-----
>> ----
>>  softmmu/vl.c        |  1 +
>>  trace-events        |  1 +
>>  util/qemu-config.c  |  4 ++++
>>  7 files changed, 70 insertions(+), 9 deletions(-)
>>
>> diff --git a/hw/core/machine.c b/hw/core/machine.c
>> index 53a99ab..7739d88 100644
>> --- a/hw/core/machine.c
>> +++ b/hw/core/machine.c
>> @@ -392,6 +392,20 @@ static void machine_set_mem_merge(Object *obj,
>> bool value, Error **errp)
>>      ms->mem_merge = value;
>>  }
>>  
>> +static bool machine_get_memfd_alloc(Object *obj, Error **errp)
>> +{
>> +    MachineState *ms = MACHINE(obj);
>> +
>> +    return ms->memfd_alloc;
>> +}
>> +
>> +static void machine_set_memfd_alloc(Object *obj, bool value, Error
>> **errp)
>> +{
>> +    MachineState *ms = MACHINE(obj);
>> +
>> +    ms->memfd_alloc = value;
>> +}
>> +
>>  static bool machine_get_usb(Object *obj, Error **errp)
>>  {
>>      MachineState *ms = MACHINE(obj);
>> @@ -829,6 +843,11 @@ 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_bool(oc, "memfd-alloc",
>> +        machine_get_memfd_alloc, machine_set_memfd_alloc);
>> +    object_class_property_set_description(oc, "memfd-alloc",
>> +        "Enable/disable allocating anonymous memory using
>> memfd_create");
>> +
>>      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 9c1c190..a57d7a0 100644
>> --- a/include/hw/boards.h
>> +++ b/include/hw/boards.h
>> @@ -327,6 +327,7 @@ struct MachineState {
>>      char *dt_compatible;
>>      bool dump_guest_core;
>>      bool mem_merge;
>> +    bool memfd_alloc;
>>      bool usb;
>>      bool usb_disabled;
>>      char *firmware;
>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index 7d47510..33c8173 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -30,6 +30,7 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
>>      "                vmport=on|off|auto controls emulation of vmport
>> (default: auto)\n"
>>      "                dump-guest-core=on|off include guest memory in
>> a core dump (default=on)\n"
>>      "                mem-merge=on|off controls memory merge support
>> (default: on)\n"
>> +    "                memfd-alloc=on|off controls allocating
>> anonymous guest RAM using memfd_create (default: off)\n"
>>      "                aes-key-wrap=on|off controls support for AES
>> key wrapping (default=on)\n"
>>      "                dea-key-wrap=on|off controls support for DEA
>> key wrapping (default=on)\n"
>>      "                suppress-vmdesc=on|off disables self-describing 
>> migration (default=off)\n"
>> @@ -76,6 +77,11 @@ SRST
>>          supported by the host, de-duplicates identical memory pages
>>          among VMs instances (enabled by default).
>>  
>> +    ``memfd-alloc=on|off``
>> +        Enables or disables allocation of anonymous guest RAM using
>> +        memfd_create.  Any associated memory-backend objects are
>> created with
>> +        share=on.  The memfd-alloc default is off.
>> +
>>      ``aes-key-wrap=on|off``
>>          Enables or disables AES key wrapping support on s390-ccw
>> hosts.
>>          This feature controls whether AES wrapping keys will be
>> created
>> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
>> index 3524c04..95e2b49 100644
>> --- a/softmmu/physmem.c
>> +++ b/softmmu/physmem.c
>> @@ -41,6 +41,7 @@
>>  #include "qemu/config-file.h"
>>  #include "qemu/error-report.h"
>>  #include "qemu/qemu-print.h"
>> +#include "qemu/memfd.h"
>>  #include "exec/memory.h"
>>  #include "exec/ioport.h"
>>  #include "sysemu/dma.h"
>> @@ -1964,35 +1965,63 @@ static void ram_block_add(RAMBlock
>> *new_block, Error **errp)
>>      const bool shared = qemu_ram_is_shared(new_block);
>>      RAMBlock *block;
>>      RAMBlock *last_block = NULL;
>> +    struct MemoryRegion *mr = new_block->mr;
>>      ram_addr_t old_ram_size, new_ram_size;
>>      Error *err = NULL;
>> +    const char *name;
>> +    void *addr = 0;
>> +    size_t maxlen;
>> +    MachineState *ms = MACHINE(qdev_get_machine());
>>  
>>      old_ram_size = last_ram_page();
>>  
>>      qemu_mutex_lock_ramlist();
>> -    new_block->offset = find_ram_offset(new_block->max_length);
>> +    maxlen = new_block->max_length;
>> +    new_block->offset = find_ram_offset(maxlen);
>>  
>>      if (!new_block->host) {
>>          if (xen_enabled()) {
>> -            xen_ram_alloc(new_block->offset, new_block->max_length,
>> -                          new_block->mr, &err);
>> +            xen_ram_alloc(new_block->offset, maxlen, new_block->mr,
>> &err);
>>              if (err) {
>>                  error_propagate(errp, err);
>>                  qemu_mutex_unlock_ramlist();
>>                  return;
>>              }
>>          } else {
>> -            new_block->host = qemu_anon_ram_alloc(new_block-
>>> max_length,
>> -                                                  &new_block->mr-
>>> align,
>> -                                                  shared,
>> noreserve);
>> -            if (!new_block->host) {
>> +            name = memory_region_name(mr);
>> +            if (ms->memfd_alloc) {
>> +                Object *parent = &mr->parent_obj;
>> +                int mfd = -1;          /* placeholder until next
>> patch */
>> +                mr->align = QEMU_VMALLOC_ALIGN;
>> +                if (mfd < 0) {
>> +                    mfd = qemu_memfd_create(name, maxlen + mr-
>>> align,
>> +                                            0, 0, 0, &err);
>> +                    if (mfd < 0) {
> 
> the error message should be propagated
> 
> Guoyi Tu
> 
>> +                        return;
>> +                    }

Will do, thanks, by setting errp directly:
     mfd = qemu_memfd_create(name, maxlen + mr->align, 0, 0, 0, errp);

- Steve