On Tue, 8 Mar 2022 01:50:11 -0500 "Michael S. Tsirkin" <[email protected]> wrote:
> 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" <[email protected]> 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 <[email protected]> > > >>> --- > > >>> 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. then another quest, is there downside to always using memfd_create without any knobs being involved? > > > >> 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 > > >> > > >> > > > >
