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Documentation: arm64: Update memory.rst for TBI

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Most of memory.rst was written very early, at a time where TBI (Top
Byte Ignore) was not enabled. Nowadays TBI0 is always enabled, and
TBI1 may be enabled, depending on the kernel configuration. This
means that VA bits 63:56 cannot generally be assumed to have any
particular value.

Regardless of TBI, TTBRx selection is done based on bit 55; update
memory.rst accordingly.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20240702091349.356008-1-kevin.brodsky@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Kevin Brodsky 2024-07-02 10:13:49 +01:00 committed by Catalin Marinas
parent 83a7eefedc
commit 5e30c16b58
1 changed files with 20 additions and 22 deletions
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42
Documentation/arch/arm64/memory.rst
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@ -18,12 +18,10 @@ ARMv8.2 adds optional support for Large Virtual Address space. This is
only available when running with a 64KB page size and expands the only available when running with a 64KB page size and expands the
number of descriptors in the first level of translation. number of descriptors in the first level of translation.
User addresses have bits 63:48 set to 0 while the kernel addresses have TTBRx selection is given by bit 55 of the virtual address. The
the same bits set to 1. TTBRx selection is given by bit 63 of the swapper_pg_dir contains only kernel (global) mappings while the user pgd
virtual address. The swapper_pg_dir contains only kernel (global) contains only user (non-global) mappings. The swapper_pg_dir address is
mappings while the user pgd contains only user (non-global) mappings. written to TTBR1 and never written to TTBR0.
The swapper_pg_dir address is written to TTBR1 and never written to
TTBR0.
AArch64 Linux memory layout with 4KB pages + 4 levels (48-bit):: AArch64 Linux memory layout with 4KB pages + 4 levels (48-bit)::
@ -65,14 +63,14 @@ Translation table lookup with 4KB pages::
+--------+--------+--------+--------+--------+--------+--------+--------+ +--------+--------+--------+--------+--------+--------+--------+--------+
|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0| |63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
+--------+--------+--------+--------+--------+--------+--------+--------+ +--------+--------+--------+--------+--------+--------+--------+--------+
| | | | | | | | | | | |
| | | | | v | | | | | v
| | | | | [11:0] in-page offset | | | | | [11:0] in-page offset
| | | | +-> [20:12] L3 index | | | | +-> [20:12] L3 index
| | | +-----------> [29:21] L2 index | | | +-----------> [29:21] L2 index
| | +---------------------> [38:30] L1 index | | +---------------------> [38:30] L1 index
| +-------------------------------> [47:39] L0 index | +-------------------------------> [47:39] L0 index
+-------------------------------------------------> [63] TTBR0/1 +----------------------------------------> [55] TTBR0/1
Translation table lookup with 64KB pages:: Translation table lookup with 64KB pages::
@ -80,14 +78,14 @@ Translation table lookup with 64KB pages::
+--------+--------+--------+--------+--------+--------+--------+--------+ +--------+--------+--------+--------+--------+--------+--------+--------+
|63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0| |63 56|55 48|47 40|39 32|31 24|23 16|15 8|7 0|
+--------+--------+--------+--------+--------+--------+--------+--------+ +--------+--------+--------+--------+--------+--------+--------+--------+
| | | | | | | | | |
| | | | v | | | | v
| | | | [15:0] in-page offset | | | | [15:0] in-page offset
| | | +----------> [28:16] L3 index | | | +----------> [28:16] L3 index
| | +--------------------------> [41:29] L2 index | | +--------------------------> [41:29] L2 index
| +-------------------------------> [47:42] L1 index (48-bit) | +-------------------------------> [47:42] L1 index (48-bit)
| [51:42] L1 index (52-bit) | [51:42] L1 index (52-bit)
+-------------------------------------------------> [63] TTBR0/1 +----------------------------------------> [55] TTBR0/1
When using KVM without the Virtualization Host Extensions, the When using KVM without the Virtualization Host Extensions, the