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diff --git a/share/man/man7/arch.7 b/share/man/man7/arch.7
--- a/share/man/man7/arch.7
+++ b/share/man/man7/arch.7
@@ -227,6 +227,56 @@
.It powerpc64le Ta 4K
.It riscv64 Ta 4K, 2M, 1G
.El
+.Ss User Address Space Layout
+.Bl -column -offset indent "riscv64 (Sv48)" "0x0001000000000000" "NNNU"
+.It Sy Architecture Ta Sy Maximum Address Ta Sy Address Space Size
+.It aarch64 Ta 0x0001000000000000 Ta 256T
+.It amd64 (LA48) Ta 0x0000800000000000 Ta 128T
+.It amd64 (LA57) Ta 0x0100000000000000 Ta 64P
+.It armv7 Ta 0xbfc00000 Ta 3G
+.It i386 Ta 0xffc00000 Ta 4G
+.It powerpc Ta 0xfffff000 Ta 4G
+.It powerpcspe Ta 0x7ffff000 Ta 2G
+.It powerpc64 Ta 0x000fffffc0000000 Ta 4P
+.It powerpc64le Ta 0x000fffffc0000000 Ta 4P
+.It riscv64 (Sv39) Ta 0x0000004000000000 Ta 256G
+.It riscv64 (Sv48) Ta 0x0000800000000000 Ta 128T
+.El
+.Pp
+The layout of a process' address space can be queried via the
+.Dv KERN_PROC_VM_LAYOUT
+.Xr sysctl(3)
+MIB.
+.Pp
+Historically, amd64 CPUs were limited to a 48-bit virtual address space.
+Newer CPUs support 5-level page tables, which extend the address space to 57
+bits (LA57 mode).
+The address space layout is determined by the CPU's support for LA57.
+The
+.Sy vm.pmap.la57
+tunable can be used to force the use of a 48-bit address space for all process,
+even on systems that support LA57.
+The
+.Sy vm.pmap.prefer_la48_uva
+tunable determines whether processes running on a LA57 system are limited to
+a 48-bit address space by default.
+Some applications make use of unused upper bits in pointer values to store
+information, and thus implicitly assume they are running in LA48 mode.
+To avoid breaking compatibility, all processes run in LA48 mode by default.
+The
+.Xr elfctl 1
+utility can be used to request LA48 or LA57 mode for specific executables.
+.Pp
+The RISC-V specification permits 3-level (Sv39), 4-level (Sv48), and
+5-level (Sv57) page tables.
+Hardware is only required to implement Sv39; implementations which support
+Sv48 must also support Sv39, and implementations which support Sv57 must also
+support Sv48.
+The
+.Sy vm.pmap.mode
+tunable can be used to select the layout.
+.Fx
+currently supports Sv39 and Sv48 and defaults to using Sv39.
.Ss Floating Point
.Bl -column -offset indent "Architecture" "float, double" "long double"
.It Sy Architecture Ta Sy float, double Ta Sy long double
@@ -424,6 +474,8 @@
it is unused outside of that scope.
.El
.Sh SEE ALSO
+.Xr elfctl 1 ,
+.Xr sysctl 3 ,
.Xr src.conf 5 ,
.Xr build 7 ,
.Xr simd 7

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