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[2003:cb:c707:8200:163d:7a08:6e61:87a5]) by smtp.gmail.com with ESMTPSA id h36-20020a05600c49a400b00382aa0b1619sm6573310wmp.45.2022.03.11.01.54.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Mar 2022 01:54:22 -0800 (PST) Message-ID: Date: Fri, 11 Mar 2022 10:54:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 To: Steve Sistare , qemu-devel@nongnu.org References: <1640199934-455149-1-git-send-email-steven.sistare@oracle.com> <1640199934-455149-11-git-send-email-steven.sistare@oracle.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH V7 10/29] machine: memfd-alloc option In-Reply-To: <1640199934-455149-11-git-send-email-steven.sistare@oracle.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, 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 , Juan Quintela , Eric Blake , "Michael S. Tsirkin" , "Dr. David Alan Gilbert" , Markus Armbruster , Zheng Chuan , Alex Williamson , Paolo Bonzini , Stefan Hajnoczi , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , "Daniel P. Berrange" , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , =?UTF-8?Q?Alex_Benn=c3=a9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 22.12.21 20:05, Steve Sistare wrote: > Allocate anonymous memory using memfd_create if the memfd-alloc machine > option is set. Hi, late to the party (thanks Igor for CCing) ... in which case it's no longer anonymous memory (because it's now MAP_SHARED). So you're converting all private memory to shared memory. For example, memory ballooning will no longer work as expected. There is no shared zeropage. KSM won't work. This brings a lot of "surprises". This patch begs for a proper description why this is required and why we cannot simply let the user handle that by properly using memory-backend-memfd manually. Especially the "memfd-alloc option" doesn't even express to a user what's actually happening and what the implications are. Long story short: this patch description has to be seriously extended. > > 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" > " 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", -- Thanks, David / dhildenb