€•=Œsphinx.addnodes”Œdocument”“”)”}”(Œ rawsource”Œ”Œchildren”]”(Œ translations”Œ LanguagesNode”“”)”}”(hhh]”(hŒ pending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ refdomain”Œstd”Œreftype”Œdoc”Œ reftarget”Œ%/translations/zh_CN/arch/arm64/memory”Œmodname”NŒ classname”NŒ refexplicit”ˆuŒtagname”hhh ubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ%/translations/zh_TW/arch/arm64/memory”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ%/translations/it_IT/arch/arm64/memory”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ%/translations/ja_JP/arch/arm64/memory”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ%/translations/ko_KR/arch/arm64/memory”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒPortuguese (Brazilian)”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ%/translations/pt_BR/arch/arm64/memory”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubh)”}”(hhh]”hŒSpanish”…””}”hh–sbah}”(h]”h ]”h"]”h$]”h&]”Œ refdomain”h)Œreftype”h+Œ reftarget”Œ%/translations/sp_SP/arch/arm64/memory”Œmodname”NŒ classname”NŒ refexplicit”ˆuh1hhh ubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h hhŒ _document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒMemory Layout on AArch64 Linux”h]”hŒMemory Layout on AArch64 Linux”…””}”(hh¼h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhh·h²hh³Œ?/var/lib/git/docbuild/linux/Documentation/arch/arm64/memory.rst”h´KubhŒ paragraph”“”)”}”(hŒ1Author: Catalin Marinas ”h]”(hŒAuthor: Catalin Marinas <”…””}”(hhÍh²hh³Nh´NubhŒ reference”“”)”}”(hŒcatalin.marinas@arm.com”h]”hŒcatalin.marinas@arm.com”…””}”(hh×h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”Œmailto:catalin.marinas@arm.com”uh1hÕhhÍubhŒ>”…””}”(hhÍh²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´Khh·h²hubhÌ)”}”(hŒÏThis document describes the virtual memory layout used by the AArch64 Linux kernel. The architecture allows up to 4 levels of translation tables with a 4KB page size and up to 3 levels with a 64KB page size.”h]”hŒÏThis document describes the virtual memory layout used by the AArch64 Linux kernel. The architecture allows up to 4 levels of translation tables with a 4KB page size and up to 3 levels with a 64KB page size.”…””}”(hhñh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´Khh·h²hubhÌ)”}”(hXSAArch64 Linux uses either 3 levels or 4 levels of translation tables with the 4KB page configuration, allowing 39-bit (512GB) or 48-bit (256TB) virtual addresses, respectively, for both user and kernel. With 64KB pages, only 2 levels of translation tables, allowing 42-bit (4TB) virtual address, are used but the memory layout is the same.”h]”hXSAArch64 Linux uses either 3 levels or 4 levels of translation tables with the 4KB page configuration, allowing 39-bit (512GB) or 48-bit (256TB) virtual addresses, respectively, for both user and kernel. With 64KB pages, only 2 levels of translation tables, allowing 42-bit (4TB) virtual address, are used but the memory layout is the same.”…””}”(hhÿh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´K hh·h²hubhÌ)”}”(hŒÁARMv8.2 adds optional support for Large Virtual Address space. This is only available when running with a 64KB page size and expands the number of descriptors in the first level of translation.”h]”hŒÁARMv8.2 adds optional support for Large Virtual Address space. This is only available when running with a 64KB page size and expands the number of descriptors in the first level of translation.”…””}”(hj h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´Khh·h²hubhÌ)”}”(hŒýTTBRx selection is given by bit 55 of the virtual address. The swapper_pg_dir contains only kernel (global) mappings while the user pgd contains only user (non-global) mappings. The swapper_pg_dir address is written to TTBR1 and never written to TTBR0.”h]”hŒýTTBRx selection is given by bit 55 of the virtual address. The swapper_pg_dir contains only kernel (global) mappings while the user pgd contains only user (non-global) mappings. The swapper_pg_dir address is written to TTBR1 and never written to TTBR0.”…””}”(hjh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´Khh·h²hubhÌ)”}”(hXzWhen using KVM without the Virtualization Host Extensions, the hypervisor maps kernel pages in EL2 at a fixed (and potentially random) offset from the linear mapping. See the kern_hyp_va macro and kvm_update_va_mask function for more details. MMIO devices such as GICv2 gets mapped next to the HYP idmap page, as do vectors when ARM64_SPECTRE_V3A is enabled for particular CPUs.”h]”hXzWhen using KVM without the Virtualization Host Extensions, the hypervisor maps kernel pages in EL2 at a fixed (and potentially random) offset from the linear mapping. See the kern_hyp_va macro and kvm_update_va_mask function for more details. MMIO devices such as GICv2 gets mapped next to the HYP idmap page, as do vectors when ARM64_SPECTRE_V3A is enabled for particular CPUs.”…””}”(hj)h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´Khh·h²hubhÌ)”}”(hŒ‡When using KVM with the Virtualization Host Extensions, no additional mappings are created, since the host kernel runs directly in EL2.”h]”hŒ‡When using KVM with the Virtualization Host Extensions, no additional mappings are created, since the host kernel runs directly in EL2.”…””}”(hj7h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´K!hh·h²hubh¶)”}”(hhh]”(h»)”}”(hŒ52-bit VA support in the kernel”h]”hŒ52-bit VA support in the kernel”…””}”(hjHh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhjEh²hh³hÊh´K%ubhÌ)”}”(hXJIf the ARMv8.2-LVA optional feature is present, and we are running with a 64KB page size; then it is possible to use 52-bits of address space for both userspace and kernel addresses. However, any kernel binary that supports 52-bit must also be able to fall back to 48-bit at early boot time if the hardware feature is not present.”h]”hXJIf the ARMv8.2-LVA optional feature is present, and we are running with a 64KB page size; then it is possible to use 52-bits of address space for both userspace and kernel addresses. However, any kernel binary that supports 52-bit must also be able to fall back to 48-bit at early boot time if the hardware feature is not present.”…””}”(hjVh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´K&hjEh²hubhÌ)”}”(hXÖThis fallback mechanism necessitates the kernel .text to be in the higher addresses such that they are invariant to 48/52-bit VAs. Due to the kasan shadow being a fraction of the entire kernel VA space, the end of the kasan shadow must also be in the higher half of the kernel VA space for both 48/52-bit. (Switching from 48-bit to 52-bit, the end of the kasan shadow is invariant and dependent on ~0UL, whilst the start address will "grow" towards the lower addresses).”h]”hXÚThis fallback mechanism necessitates the kernel .text to be in the higher addresses such that they are invariant to 48/52-bit VAs. Due to the kasan shadow being a fraction of the entire kernel VA space, the end of the kasan shadow must also be in the higher half of the kernel VA space for both 48/52-bit. (Switching from 48-bit to 52-bit, the end of the kasan shadow is invariant and dependent on ~0UL, whilst the start address will “grow†towards the lower addresses).”…””}”(hjdh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´K,hjEh²hubhÌ)”}”(hXIn order to optimise phys_to_virt and virt_to_phys, the PAGE_OFFSET is kept constant at 0xFFF0000000000000 (corresponding to 52-bit), this obviates the need for an extra variable read. The physvirt offset and vmemmap offsets are computed at early boot to enable this logic.”h]”hXIn order to optimise phys_to_virt and virt_to_phys, the PAGE_OFFSET is kept constant at 0xFFF0000000000000 (corresponding to 52-bit), this obviates the need for an extra variable read. The physvirt offset and vmemmap offsets are computed at early boot to enable this logic.”…””}”(hjrh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´K4hjEh²hubhÌ)”}”(hŒÇAs a single binary will need to support both 48-bit and 52-bit VA spaces, the VMEMMAP must be sized large enough for 52-bit VAs and also must be sized large enough to accommodate a fixed PAGE_OFFSET.”h]”hŒÇAs a single binary will need to support both 48-bit and 52-bit VA spaces, the VMEMMAP must be sized large enough for 52-bit VAs and also must be sized large enough to accommodate a fixed PAGE_OFFSET.”…””}”(hj€h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´K:hjEh²hubhÌ)”}”(hŒ’Most code in the kernel should not need to consider the VA_BITS, for code that does need to know the VA size the variables are defined as follows:”h]”hŒ’Most code in the kernel should not need to consider the VA_BITS, for code that does need to know the VA size the variables are defined as follows:”…””}”(hjŽh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´K>hjEh²hubhÌ)”}”(hŒ;VA_BITS constant the *maximum* VA space size”h]”(hŒ$VA_BITS constant the ”…””}”(hjœh²hh³Nh´NubhŒemphasis”“”)”}”(hŒ *maximum*”h]”hŒmaximum”…””}”(hj¦h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¤hjœubhŒ VA space size”…””}”(hjœh²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´KBhjEh²hubhÌ)”}”(hŒ;VA_BITS_MIN constant the *minimum* VA space size”h]”(hŒ$VA_BITS_MIN constant the ”…””}”(hj¾h²hh³Nh´Nubj¥)”}”(hŒ *minimum*”h]”hŒminimum”…””}”(hjÆh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¤hj¾ubhŒ VA space size”…””}”(hj¾h²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´KDhjEh²hubhÌ)”}”(hŒ:vabits_actual variable the *actual* VA space size”h]”(hŒ$vabits_actual variable the ”…””}”(hjÞh²hh³Nh´Nubj¥)”}”(hŒ*actual*”h]”hŒactual”…””}”(hjæh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j¤hjÞubhŒ VA space size”…””}”(hjÞh²hh³Nh´Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´KFhjEh²hubhÌ)”}”(hŒ™Maximum and minimum sizes can be useful to ensure that buffers are sized large enough or that addresses are positioned close enough for the "worst" case.”h]”hŒMaximum and minimum sizes can be useful to ensure that buffers are sized large enough or that addresses are positioned close enough for the “worst†case.”…””}”(hjþh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´KIhjEh²hubeh}”(h]”Œbit-va-support-in-the-kernel”ah ]”h"]”Œ52-bit va support in the kernel”ah$]”h&]”uh1hµhh·h²hh³hÊh´K%ubh¶)”}”(hhh]”(h»)”}”(hŒ52-bit userspace VAs”h]”hŒ52-bit userspace VAs”…””}”(hjh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hºhjh²hh³hÊh´KNubhÌ)”}”(hŒ¼To maintain compatibility with software that relies on the ARMv8.0 VA space maximum size of 48-bits, the kernel will, by default, return virtual addresses to userspace from a 48-bit range.”h]”hŒ¼To maintain compatibility with software that relies on the ARMv8.0 VA space maximum size of 48-bits, the kernel will, by default, return virtual addresses to userspace from a 48-bit range.”…””}”(hj%h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´KOhjh²hubhÌ)”}”(hŒ{Software can "opt-in" to receiving VAs from a 52-bit space by specifying an mmap hint parameter that is larger than 48-bit.”h]”hŒSoftware can “opt-in†to receiving VAs from a 52-bit space by specifying an mmap hint parameter that is larger than 48-bit.”…””}”(hj3h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´KShjh²hubhÌ)”}”(hŒ For example:”h]”hŒ For example:”…””}”(hjAh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´KVhjh²hubhŒ literal_block”“”)”}”(hŒ7maybe_high_address = mmap(~0UL, size, prot, flags,...);”h]”hŒ7maybe_high_address = mmap(~0UL, size, prot, flags,...);”…””}”hjQsbah}”(h]”h ]”h"]”h$]”h&]”Œ xml:space”Œpreserve”Œforce”‰Œlanguage”Œc”Œhighlight_args”}”uh1jOh³hÊh´KXhjh²hubhÌ)”}”(hŒ‡It is also possible to build a debug kernel that returns addresses from a 52-bit space by enabling the following kernel config options:”h]”hŒ‡It is also possible to build a debug kernel that returns addresses from a 52-bit space by enabling the following kernel config options:”…””}”(hjfh²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´K\hjh²hubjP)”}”(hŒ-CONFIG_EXPERT=y && CONFIG_ARM64_FORCE_52BIT=y”h]”hŒ-CONFIG_EXPERT=y && CONFIG_ARM64_FORCE_52BIT=y”…””}”hjtsbah}”(h]”h ]”h"]”h$]”h&]”j_j`ja‰jbŒsh”jd}”uh1jOh³hÊh´K_hjh²hubhÌ)”}”(hŒgNote that this option is only intended for debugging applications and should not be used in production.”h]”hŒgNote that this option is only intended for debugging applications and should not be used in production.”…””}”(hj„h²hh³Nh´Nubah}”(h]”h ]”h"]”h$]”h&]”uh1hËh³hÊh´Kchjh²hubeh}”(h]”Œbit-userspace-vas”ah ]”h"]”Œ52-bit userspace vas”ah$]”h&]”uh1hµhh·h²hh³hÊh´KNubeh}”(h]”Œmemory-layout-on-aarch64-linux”ah ]”h"]”Œmemory layout on aarch64 linux”ah$]”h&]”uh1hµhhh²hh³hÊh´Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”hÊuh1hŒcurrent_source”NŒ current_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(hºNŒ generator”NŒ datestamp”NŒ source_link”NŒ source_url”NŒ toc_backlinks”Œentry”Œfootnote_backlinks”KŒ sectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒ strip_classes”NŒ 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