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| author | Kevin Brodsky <kevin.brodsky@arm.com> | 2024-07-02 11:13:49 +0200 |
|---|---|---|
| committer | Catalin Marinas <catalin.marinas@arm.com> | 2024-07-04 16:10:31 +0200 |
| commit | 5e30c16b58a486ff8700512e43eac9949c32621b (patch) | |
| tree | 3be4547101fb7fedf1484b7495043299e5e3c19c | |
| parent | Linux 6.10-rc3 (diff) | |
| download | linux-5e30c16b58a486ff8700512e43eac9949c32621b.tar.xz linux-5e30c16b58a486ff8700512e43eac9949c32621b.zip | |
Documentation: arm64: Update memory.rst for TBI
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>
| -rw-r--r-- | Documentation/arch/arm64/memory.rst | 42 |
1 files changed, 20 insertions, 22 deletions
diff --git a/Documentation/arch/arm64/memory.rst b/Documentation/arch/arm64/memory.rst index 55a55f30eed8..8a658984b8bb 100644 --- a/Documentation/arch/arm64/memory.rst +++ b/Documentation/arch/arm64/memory.rst @@ -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 number of descriptors in the first level of translation. -User addresses have bits 63:48 set to 0 while the kernel addresses have -the same bits set to 1. TTBRx selection is given by bit 63 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. +TTBRx 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. 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| +--------+--------+--------+--------+--------+--------+--------+--------+ - | | | | | | - | | | | | v - | | | | | [11:0] in-page offset - | | | | +-> [20:12] L3 index - | | | +-----------> [29:21] L2 index - | | +---------------------> [38:30] L1 index - | +-------------------------------> [47:39] L0 index - +-------------------------------------------------> [63] TTBR0/1 + | | | | | | + | | | | | v + | | | | | [11:0] in-page offset + | | | | +-> [20:12] L3 index + | | | +-----------> [29:21] L2 index + | | +---------------------> [38:30] L1 index + | +-------------------------------> [47:39] L0 index + +----------------------------------------> [55] TTBR0/1 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| +--------+--------+--------+--------+--------+--------+--------+--------+ - | | | | | - | | | | v - | | | | [15:0] in-page offset - | | | +----------> [28:16] L3 index - | | +--------------------------> [41:29] L2 index - | +-------------------------------> [47:42] L1 index (48-bit) - | [51:42] L1 index (52-bit) - +-------------------------------------------------> [63] TTBR0/1 + | | | | | + | | | | v + | | | | [15:0] in-page offset + | | | +----------> [28:16] L3 index + | | +--------------------------> [41:29] L2 index + | +-------------------------------> [47:42] L1 index (48-bit) + | [51:42] L1 index (52-bit) + +----------------------------------------> [55] TTBR0/1 When using KVM without the Virtualization Host Extensions, the |