On Thu, 3 Mar 2022 12:21:15 -0500 "Michael S. Tsirkin" <m...@redhat.com> wrote:
> On Wed, Dec 22, 2021 at 11:05:15AM -0800, Steve Sistare wrote: > > Allocate anonymous memory using memfd_create if the memfd-alloc machine > > option is set. > > > > Signed-off-by: Steve Sistare <steven.sist...@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" > > Question: are there any disadvantages associated with using > memfd_create? I guess we are using up an fd, but that seems minor. Any > reason not to set to on by default? maybe with a fallback option to > disable that? > > I am concerned that it's actually a kind of memory backend, this flag > seems to instead be closer to the deprecated mem-prealloc. E.g. > it does not work with a mem path, does it? (mem path and mem-prealloc are transparently aliased to used memory backend if I recall it right.) Steve, For allocating guest RAM, we switched exclusively to using memory-backends including initial guest RAM (-m size option) and we have hostmem-memfd that uses memfd_create() and I'd rather avoid adding random knobs to machine for tweaking how RAM should be allocated, we have memory backends for this, so this patch begs the question: why hostmem-memfd is not sufficient? (patch description is rather lacking on rationale behind the patch) > > > > " 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) { > > + 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 > >