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Tsirkin" To: Steven Sistare Subject: Re: [PATCH V7 10/29] machine: memfd-alloc option Message-ID: <20220307184045-mutt-send-email-mst@kernel.org> References: <1640199934-455149-1-git-send-email-steven.sistare@oracle.com> <1640199934-455149-11-git-send-email-steven.sistare@oracle.com> <20220303121534-mutt-send-email-mst@kernel.org> <20220304114124.6fe97646@redhat.com> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jason Zeng , Markus Armbruster , Juan Quintela , Eric Blake , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , "Daniel P. Berrange" , qemu-devel@nongnu.org, Zheng Chuan , Alex Williamson , Paolo Bonzini , Stefan Hajnoczi , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Igor Mammedov , Alex =?iso-8859-1?Q?Benn=E9e?= , "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Mar 07, 2022 at 09:41:44AM -0500, Steven Sistare wrote: > On 3/4/2022 5:41 AM, Igor Mammedov wrote: > > On Thu, 3 Mar 2022 12:21:15 -0500 > > "Michael S. Tsirkin" 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 > >>> --- > >>> 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? > > Old Linux host kernels, circa 4.1, do not support huge pages for shared memory. > Also, the tunable to enable huge pages for share memory is different than for > anon memory, so there could be performance loss if it is not set correctly. > /sys/kernel/mm/transparent_hugepage/enabled > vs > /sys/kernel/mm/transparent_hugepage/shmem_enabled I guess we can test this when launching the VM, and select a good default. > It might make sense to use memfd_create by default for the secondary segments. Well there's also KSM now you mention it. > >> 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? > > One can still define a memory backend with mempath to create the main ram segment, > though it must be some form of shared to work with live update. Indeed, I would > expect most users to specify an explicit memory backend for it. The secondary > segments would still use memfd_create. > > > (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) > > There is currently no way to specify memory backends for the secondary memory > segments (vram, roms, etc), and IMO it would be onerous to specify a backend for > each of them. On x86_64, these include pc.bios, vga.vram, pc.rom, vga.rom, > /rom@etc/acpi/tables, /rom@etc/table-loader, /rom@etc/acpi/rsdp. > > - Steve > > >>> " 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 > >> > >> > >