The legacy 32-bit SMBIOS entry point has little use on AARCH64 systems, since many such systems have no 32-bit addressable physical RAM, and so OSes that implement SMBIOS will have to be able to deal with the 64-bit entry point anyway.
Given that the OS will map main memory in 1 GB chunks if it can, and that punching a page sized hole (e.g., for SMBIOS data) into it will result in the whole 1 GB chunk being mapped using 2 MB and 4 KB blocks instead, it is important to group memory reservations from the OS as much as we can, and allocating below 4 GB for no good reason interferes with that. This is especially important under virtualization, considering that each *level* of lookup at stage 1 (the guest virtual page table) will result in a full page table walk at stage 2 (the guest PA to host PA mapping). So expose only the 64-bit entry point when the SMBIOS tables adhere to version 3.0 or later. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Ard Biesheuvel <[email protected]> --- v2: - reworked commit log and PCD comment per Laszlo's feedback, primarily to clarify that the PCD only takes effect if the actual version of the SMBIOS entry point and tables is v3.0 or later - move PCD definition to existing [PcdsFixedAtBuild.AARCH64] section ArmVirtPkg/ArmVirtQemu.dsc | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc index 7c6419fbb92f..725de864aebe 100644 --- a/ArmVirtPkg/ArmVirtQemu.dsc +++ b/ArmVirtPkg/ArmVirtQemu.dsc @@ -169,6 +169,14 @@ [PcdsFixedAtBuild.AARCH64] # support anything bigger, even if the host hardware does gEmbeddedTokenSpaceGuid.PcdPrePiCpuMemorySize|40 + # Clearing BIT0 in this PCD prevents installing a 32-bit SMBIOS entry point, + # if the entry point version is >= 3.0. AARCH64 OSes cannot assume the + # presence of the 32-bit entry point anyway (because many AARCH64 systems + # don't have 32-bit addressable physical RAM), and the additional allocations + # below 4 GB needlessly fragment the memory map. So expose the 64-bit entry + # point only, for entry point versions >= 3.0. + gEfiMdeModulePkgTokenSpaceGuid.PcdSmbiosEntryPointProvideMethod|0x2 + [PcdsDynamicDefault.common] ## If TRUE, OvmfPkg/AcpiPlatformDxe will not wait for PCI # enumeration to complete before installing ACPI tables. -- 2.5.0 _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
