€•1<      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ%/translations/zh_CN/arch/arm64/memory”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/zh_TW/arch/arm64/memory”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/it_IT/arch/arm64/memory”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/ja_JP/arch/arm64/memory”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/ko_KR/arch/arm64/memory”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/sp_SP/arch/arm64/memory”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒMemory Layout on AArch64 Linux”h]”hŒMemory Layout on AArch64 Linux”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒ?/var/lib/git/docbuild/linux/Documentation/arch/arm64/memory.rst”h KubhŒ	paragraph”“”)”}”(hŒ1Author: Catalin Marinas <catalin.marinas@arm.com>”h]”(hŒAuthor: Catalin Marinas <”…””}”(hh¹hžhhŸNh NubhŒ	reference”“”)”}”(hŒcatalin.marinas@arm.com”h]”hŒcatalin.marinas@arm.com”…””}”(hhÃhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”Œmailto:catalin.marinas@arm.com”uh1hÁhh¹ubhŒ>”…””}”(hh¹hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒÏThis document describes the virtual memory layout used by the AArch64
Linux kernel. The architecture allows up to 4 levels of translation
tables with a 4KB page size and up to 3 levels with a 64KB page size.”h]”hŒÏThis document describes the virtual memory layout used by the AArch64
Linux kernel. The architecture allows up to 4 levels of translation
tables with a 4KB page size and up to 3 levels with a 64KB page size.”…””}”(hhÝhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hXS  AArch64 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]”hXS  AArch64 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hëhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒÁARMv8.2 adds optional support for Large Virtual Address space. This is
only available when running with a 64KB page size and expands the
number of descriptors in the first level of translation.”h]”hŒÁARMv8.2 adds optional support for Large Virtual Address space. This is
only available when running with a 64KB page size and expands the
number of descriptors in the first level of translation.”…””}”(hhùhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒýTTBRx 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]”hŒýTTBRx 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j  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hXz  When using KVM without the Virtualization Host Extensions, the
hypervisor maps kernel pages in EL2 at a fixed (and potentially
random) offset from the linear mapping. See the kern_hyp_va macro and
kvm_update_va_mask function for more details. MMIO devices such as
GICv2 gets mapped next to the HYP idmap page, as do vectors when
ARM64_SPECTRE_V3A is enabled for particular CPUs.”h]”hXz  When using KVM without the Virtualization Host Extensions, the
hypervisor maps kernel pages in EL2 at a fixed (and potentially
random) offset from the linear mapping. See the kern_hyp_va macro and
kvm_update_va_mask function for more details. MMIO devices such as
GICv2 gets mapped next to the HYP idmap page, as do vectors when
ARM64_SPECTRE_V3A is enabled for particular CPUs.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hŒ‡When using KVM with the Virtualization Host Extensions, no additional
mappings are created, since the host kernel runs directly in EL2.”h]”hŒ‡When using KVM with the Virtualization Host Extensions, no additional
mappings are created, since the host kernel runs directly in EL2.”…””}”(hj#  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K!hh£hžhubh¢)”}”(hhh]”(h§)”}”(hŒ52-bit VA support in the kernel”h]”hŒ52-bit VA support in the kernel”…””}”(hj4  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj1  hžhhŸh¶h K%ubh¸)”}”(hXJ  If 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]”hXJ  If 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jB  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K&hj1  hžhubh¸)”}”(hXÖ  This fallback mechanism necessitates the kernel .text to be in the
higher addresses such that they are invariant to 48/52-bit VAs. Due
to the kasan shadow being a fraction of the entire kernel VA space,
the end of the kasan shadow must also be in the higher half of the
kernel VA space for both 48/52-bit. (Switching from 48-bit to 52-bit,
the end of the kasan shadow is invariant and dependent on ~0UL,
whilst the start address will "grow" towards the lower addresses).”h]”hXÚ  This fallback mechanism necessitates the kernel .text to be in the
higher addresses such that they are invariant to 48/52-bit VAs. Due
to the kasan shadow being a fraction of the entire kernel VA space,
the end of the kasan shadow must also be in the higher half of the
kernel VA space for both 48/52-bit. (Switching from 48-bit to 52-bit,
the end of the kasan shadow is invariant and dependent on ~0UL,
whilst the start address will â€œgrowâ€ towards the lower addresses).”…””}”(hjP  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K,hj1  hžhubh¸)”}”(hX  In 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]”hX  In 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j^  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K4hj1  hžhubh¸)”}”(hŒÇAs a single binary will need to support both 48-bit and 52-bit VA
spaces, the VMEMMAP must be sized large enough for 52-bit VAs and
also must be sized large enough to accommodate a fixed PAGE_OFFSET.”h]”hŒÇAs a single binary will need to support both 48-bit and 52-bit VA
spaces, the VMEMMAP must be sized large enough for 52-bit VAs and
also must be sized large enough to accommodate a fixed PAGE_OFFSET.”…””}”(hjl  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K:hj1  hžhubh¸)”}”(hŒ’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]”hŒ’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jz  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K>hj1  hžhubh¸)”}”(hŒ;VA_BITS         constant        the *maximum* VA space size”h]”(hŒ$VA_BITS         constant        the ”…””}”(hjˆ  hžhhŸNh NubhŒemphasis”“”)”}”(hŒ	*maximum*”h]”hŒmaximum”…””}”(hj’  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjˆ  ubhŒ VA space size”…””}”(hjˆ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KBhj1  hžhubh¸)”}”(hŒ;VA_BITS_MIN     constant        the *minimum* VA space size”h]”(hŒ$VA_BITS_MIN     constant        the ”…””}”(hjª  hžhhŸNh Nubj‘  )”}”(hŒ	*minimum*”h]”hŒminimum”…””}”(hj²  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjª  ubhŒ VA space size”…””}”(hjª  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KDhj1  hžhubh¸)”}”(hŒ:vabits_actual   variable        the *actual* VA space size”h]”(hŒ$vabits_actual   variable        the ”…””}”(hjÊ  hžhhŸNh Nubj‘  )”}”(hŒ*actual*”h]”hŒactual”…””}”(hjÒ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1j  hjÊ  ubhŒ VA space size”…””}”(hjÊ  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KFhj1  hžhubh¸)”}”(hŒ™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]”hŒMaximum and minimum sizes can be useful to ensure that buffers are
sized large enough or that addresses are positioned close enough for
the â€œworstâ€ case.”…””}”(hjê  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KIhj1  hžhubeh}”(h]”Œbit-va-support-in-the-kernel”ah ]”h"]”Œ52-bit va support in the kernel”ah$]”h&]”uh1h¡hh£hžhhŸh¶h K%ubh¢)”}”(hhh]”(h§)”}”(hŒ52-bit userspace VAs”h]”hŒ52-bit userspace VAs”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj   hžhhŸh¶h KNubh¸)”}”(hŒ¼To maintain compatibility with software that relies on the ARMv8.0
VA space maximum size of 48-bits, the kernel will, by default,
return virtual addresses to userspace from a 48-bit range.”h]”hŒ¼To maintain compatibility with software that relies on the ARMv8.0
VA space maximum size of 48-bits, the kernel will, by default,
return virtual addresses to userspace from a 48-bit range.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KOhj   hžhubh¸)”}”(hŒ{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]”hŒSoftware can â€œopt-inâ€ to receiving VAs from a 52-bit space by
specifying an mmap hint parameter that is larger than 48-bit.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KShj   hžhubh¸)”}”(hŒFor example:”h]”hŒFor example:”…””}”(hj-  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KVhj   hžhubhŒliteral_block”“”)”}”(hŒ7maybe_high_address = mmap(~0UL, size, prot, flags,...);”h]”hŒ7maybe_high_address = mmap(~0UL, size, prot, flags,...);”…””}”hj=  sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”Œforce”‰Œlanguage”Œc”Œhighlight_args”}”uh1j;  hŸh¶h KXhj   hžhubh¸)”}”(hŒ‡It is also possible to build a debug kernel that returns addresses
from a 52-bit space by enabling the following kernel config options:”h]”hŒ‡It is also possible to build a debug kernel that returns addresses
from a 52-bit space by enabling the following kernel config options:”…””}”(hjR  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K\hj   hžhubj<  )”}”(hŒ-CONFIG_EXPERT=y && CONFIG_ARM64_FORCE_52BIT=y”h]”hŒ-CONFIG_EXPERT=y && CONFIG_ARM64_FORCE_52BIT=y”…””}”hj`  sbah}”(h]”h ]”h"]”h$]”h&]”jK  jL  jM  ‰jN  Œsh”jP  }”uh1j;  hŸh¶h K_hj   hžhubh¸)”}”(hŒgNote that this option is only intended for debugging applications
and should not be used in production.”h]”hŒgNote that this option is only intended for debugging applications
and should not be used in production.”…””}”(hjp  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kchj   hžhubeh}”(h]”Œbit-userspace-vas”ah ]”h"]”Œ52-bit userspace vas”ah$]”h&]”uh1h¡hh£hžhhŸh¶h KNubeh}”(h]”Œmemory-layout-on-aarch64-linux”ah ]”h"]”Œmemory layout on aarch64 linux”ah$]”h&]”uh1h¡hhhžhhŸh¶h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h¶uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¦NŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
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