On Thu, 11 Jul 2024 10:19:27 +0200 Philippe Mathieu-Daudé <phi...@linaro.org> wrote:
> Hi Igor, > > On 11/7/24 09:48, Igor Mammedov wrote: > > Currently SMBIOS maximum memory device chunk is capped at 16Gb, > > which is fine for the most cases (QEMU uses it to describe initial > > RAM (type 17 SMBIOS table entries)). > > However when starting guest with terabytes of RAM this leads to > > too many memory device structures, which eventually upsets linux > > kernel as it reserves only 64K for these entries and when that > > border is crossed out it runs out of reserved memory. > > > > Instead of partitioning initial RAM on 16Gb chunks, use maximum > > possible chunk size that SMBIOS spec allows[1]. Which lets > > encode RAM in Mb units in uint32_t-1 field (upto 2047Tb). > > As result initial RAM will generate only one type 17 structure > > until host/guest reach ability to use more RAM in the future. > > > > Compat changes: > > We can't unconditionally change chunk size as it will break > > QEMU<->guest ABI (and migration). Thus introduce a new machine class > > field that would let older versioned machines to use 16Gb chunks > > while new machine type could use maximum possible chunk size. > > > > While it might seem to be risky to rise max entry size this much > > (much beyond of what current physical RAM modules support), > > I'd not expect it causing much issues, modulo uncovering bugs > > in software running within guest. And those should be fixed > > on guest side to handle SMBIOS spec properly, especially if > > guest is expected to support so huge RAM configs. > > In worst case, QEMU can reduce chunk size later if we would > > care enough about introducing a workaround for some 'unfixable' > > guest OS, either by fixing up the next machine type or > > giving users a CLI option to customize it. > > > > 1) SMBIOS 3.1.0 7.18.5 Memory Device — Extended Size > > > > PS: > > * tested on 8Tb host with RHEL6 guest, which seems to parse > > type 17 SMBIOS table entries correctly (according to 'dmidecode'). > > > > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > > --- > > include/hw/boards.h | 4 ++++ > > hw/arm/virt.c | 1 + > > hw/core/machine.c | 1 + > > hw/i386/pc_piix.c | 1 + > > hw/i386/pc_q35.c | 1 + > > hw/smbios/smbios.c | 11 ++++++----- > > 6 files changed, 14 insertions(+), 5 deletions(-) > > > > diff --git a/include/hw/boards.h b/include/hw/boards.h > > index ef6f18f2c1..48ff6d8b93 100644 > > --- a/include/hw/boards.h > > +++ b/include/hw/boards.h > > @@ -237,6 +237,9 @@ typedef struct { > > * purposes only. > > * Applies only to default memory backend, i.e., explicit memory > > backend > > * wasn't used. > > + * @smbios_memory_device_size: > > + * Default size of memory device, > > + * SMBIOS 3.1.0 "7.18 Memory Device (Type 17)" > > */ > > struct MachineClass { > > /*< private >*/ > > @@ -304,6 +307,7 @@ struct MachineClass { > > const CPUArchIdList *(*possible_cpu_arch_ids)(MachineState *machine); > > int64_t (*get_default_cpu_node_id)(const MachineState *ms, int idx); > > ram_addr_t (*fixup_ram_size)(ram_addr_t size); > > + uint64_t smbios_memory_device_size; > > Quick notes since I'm on holidays (not meant to block this patch): > > - How will evolve this machine class property in the context of > a heterogeneous machine (i.e. x86_64 cores and 1 riscv32 one)? I'm not aware of a SMBIOS spec (3.x) that cares about that heterogeneous setup yet. Are there anything in that area exists yet? > - Should this become a SmbiosProviderInterface later? if/when SMBIOS does get there (heterogeneous machines), introducing an interface might make a sense. > > > }; > > > > /** > > diff --git a/hw/arm/virt.c b/hw/arm/virt.c > > index b0c68d66a3..719e83e6a1 100644 > > --- a/hw/arm/virt.c > > +++ b/hw/arm/virt.c > > @@ -3308,6 +3308,7 @@ DEFINE_VIRT_MACHINE_AS_LATEST(9, 1) > > static void virt_machine_9_0_options(MachineClass *mc) > > { > > virt_machine_9_1_options(mc); > > + mc->smbios_memory_device_size = 16 * GiB; > > compat_props_add(mc->compat_props, hw_compat_9_0, hw_compat_9_0_len); > > } > > DEFINE_VIRT_MACHINE(9, 0) > > [...] >