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

[Steven Sistare]

On 2/24/2022 12:56 PM, Dr. David Alan Gilbert wrote:
> * Steve Sistare (steven.sistare@oracle.com) wrote:
>> Allocate anonymous memory using memfd_create if the memfd-alloc machine
>> option is set.
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> 
> So other than the minor error nit that Guoyi spotted, I think this is
> pretty good,  one other comment below:
> 
>> ---
>>  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;
> 
> You could move some of these down to the top of the block you're using
> them.

Will do.

One question:  I added this to shorten lines and make my code additions more 
readable:

    size_t maxlen;
    maxlen = new_block->max_length;

However, I did not change new_block->max_length to maxlen in the second half of 
the
function which I did not modify, to avoid noise in the patch that is unrelated 
to cpr.
Making those changes would shorten a few multi-liners.  What is your preference 
-- 
make those changes or not?

- Steve

>> +    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) {
>> +                        return;
>> +                    }
>> +                }
>> +                qemu_set_cloexec(mfd);
>> +                /* The memory backend already set its desired flags. */
>> +                if (!object_dynamic_cast(parent, TYPE_MEMORY_BACKEND)) {
>> +                    new_block->flags |= RAM_SHARED;
>> +                }
>> +                addr = file_ram_alloc(new_block, maxlen, mfd,
>> +                                      false, false, 0, errp);
>> +                trace_anon_memfd_alloc(name, maxlen, addr, mfd);
>> +            } else {
>> +                addr = qemu_anon_ram_alloc(maxlen, &mr->align,
>> +                                           shared, noreserve);
>> +            }
>> +
>> +            if (!addr) {
>>                  error_setg_errno(errp, errno,
>>                                   "cannot set up guest memory '%s'",
>> -                                 memory_region_name(new_block->mr));
>> +                                 name);
>>                  qemu_mutex_unlock_ramlist();
>>                  return;
>>              }
>> -            memory_try_enable_merging(new_block->host, 
>> new_block->max_length);
>> +            memory_try_enable_merging(addr, maxlen);
>> +            new_block->host = addr;
>>          }
>>      }
>>  
>> diff --git a/softmmu/vl.c b/softmmu/vl.c
>> index 620a1f1..ab3648a 100644
>> --- a/softmmu/vl.c
>> +++ b/softmmu/vl.c
>> @@ -2440,6 +2440,7 @@ static void create_default_memdev(MachineState *ms, 
>> const char *path)
>>          object_property_set_str(obj, "mem-path", path, &error_fatal);
>>      }
>>      object_property_set_int(obj, "size", ms->ram_size, &error_fatal);
>> +    object_property_set_bool(obj, "share", ms->memfd_alloc, &error_fatal);
>>      object_property_add_child(object_get_objects_root(), mc->default_ram_id,
>>                                obj);
>>      /* Ensure backend's memory region name is equal to mc->default_ram_id */
>> diff --git a/trace-events b/trace-events
>> index a637a61..770a9ac 100644
>> --- a/trace-events
>> +++ b/trace-events
>> @@ -45,6 +45,7 @@ ram_block_discard_range(const char *rbname, void *hva, 
>> size_t length, bool need_
>>  # accel/tcg/cputlb.c
>>  memory_notdirty_write_access(uint64_t vaddr, uint64_t ram_addr, unsigned 
>> size) "0x%" PRIx64 " ram_addr 0x%" PRIx64 " size %u"
>>  memory_notdirty_set_dirty(uint64_t vaddr) "0x%" PRIx64
>> +anon_memfd_alloc(const char *name, size_t size, void *ptr, int fd) "%s size 
>> %zu ptr %p fd %d"
>>  
>>  # gdbstub.c
>>  gdbstub_op_start(const char *device) "Starting gdbstub using device %s"
>> diff --git a/util/qemu-config.c b/util/qemu-config.c
>> index 436ab63..3606e5c 100644
>> --- a/util/qemu-config.c
>> +++ b/util/qemu-config.c
>> @@ -207,6 +207,10 @@ static QemuOptsList machine_opts = {
>>              .type = QEMU_OPT_BOOL,
>>              .help = "enable/disable memory merge support",
>>          },{
>> +            .name = "memfd-alloc",
>> +            .type = QEMU_OPT_BOOL,
>> +            .help = "enable/disable memfd_create for anonymous memory",
>> +        },{
>>              .name = "usb",
>>              .type = QEMU_OPT_BOOL,
>>              .help = "Set on/off to enable/disable usb",
>> -- 
>> 1.8.3.1
>>