Documentation/arm64: add memory layout with 4KB pages + VA39-bit
PATCH 1/1 Documentation/arm64: add memory layout with 4KB pages + VA39-bit
The 4KB pages + 3 levels (39-bit) combination is also widely used in arm64 world, add the memory layout description for this combination.
--- Documentation/arm64/memory.rst | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)
Documentation/arm64/memory.rst +17 -0
@@ -26,6 +26,23 @@ The swapper_pg_dir address is written to TTBR1 and never written to TTBR0. +AArch64 Linux memory layout with 4KB pages + 3 levels (39-bit):: + Start End Size Use + ----------------------------------------------------------------------- + 0000000000000000 0000007fffffffff 512GB user + ffffff8000000000 ffffffbfffffffff 256GB kernel logical memory map + [ffffffb000000000 ffffffbfffffffff] 64GB [kasan shadow region] + ffffffc000000000 ffffffc007ffffff 128MB bpf jit region + ffffffc008000000 ffffffc00fffffff 128MB modules + ffffffc010000000 fffffffdefffffff 253440MB vmalloc + fffffffdf0000000 fffffffdfdffffff 224MB fixed mappings (top down) + fffffffdfe000000 fffffffdfe7fffff 8MB [guard region] + fffffffdfe800000 fffffffdff7fffff 16MB PCI I/O space + fffffffdff800000 fffffffdffffffff 8MB [guard region] + fffffffe00000000 ffffffffefffffff 4GB vmemmap + ffffffff00000000 ffffffffffffffff 4GB [guard region] + + AArch64 Linux memory layout with 4KB pages + 4 levels (48-bit):: Start End Size Use
Signature · 1 line
2.33.0
Quoted 21 lines · Jisheng Zhang
The 4KB pages + 3 levels (39-bit) combination is also widely used in arm64 world, add the memory layout description for this combination.
Signed-off-by Jisheng Zhang <[email protected]>--- Documentation/arm64/memory.rst | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)Documentation/arm64/memory.rst +5
-0@@ -26,6 +26,23 @@ The swapper_pg_dir address is written to TTBR1 and never written to TTBR0. +AArch64 Linux memory layout with 4KB pages + 3 levels (39-bit):: + Start End Size Use + ----------------------------------------------------------------------- + 0000000000000000 0000007fffffffff 512GB user + ffffff8000000000 ffffffbfffffffff 256GB kernel logical memory map
Documentation/arm64/memory.rst The swapper_pg_dir address is written to TTBR1 and never written to · line 43
Quoted 10 lines
Documentation/arm64/memory.rst +10
-0+ [ffffffb000000000 ffffffbfffffffff] 64GB [kasan shadow region] + ffffffc000000000 ffffffc007ffffff 128MB bpf jit region + ffffffc008000000 ffffffc00fffffff 128MB modules + ffffffc010000000 fffffffdefffffff 253440MB vmalloc + fffffffdf0000000 fffffffdfdffffff 224MB fixed mappings (top down) + fffffffdfe000000 fffffffdfe7fffff 8MB [guard region] + fffffffdfe800000 fffffffdff7fffff 16MB PCI I/O space + fffffffdff800000 fffffffdffffffff 8MB [guard region] + fffffffe00000000 ffffffffefffffff 4GB vmemmap + ffffffff00000000 ffffffffffffffff 4GB [guard region]
I wouldn't bother maintaining these. There are other combinations that people may use. The 4KB + 48-bit VA is defconfig while 64KB + 52-bit was more interesting, so we thought it would be useful.
I'm more inclined to remove them altogether and maybe just add some high-level ascii art as per the log of commit f4693c2716b3 ("arm64: mm:
extend linear region for 52-bit VA configurations").
Signature · 1 line
Catalin
Quoted 30 lines · On Wed, 6 Oct 2021 18:14:38 +0100 Catalin Marinas <[email protected]>…
Quoted 27 lines · Jisheng Zhang
The 4KB pages + 3 levels (39-bit) combination is also widely used in arm64 world, add the memory layout description for this combination.
Signed-off-by Jisheng Zhang <[email protected]>--- Documentation/arm64/memory.rst | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)Documentation/arm64/memory.rst +11
-0@@ -26,6 +26,23 @@ The swapper_pg_dir address is written to TTBR1 and never written to TTBR0. +AArch64 Linux memory layout with 4KB pages + 3 levels (39-bit):: + Start End Size Use + ----------------------------------------------------------------------- + 0000000000000000 0000007fffffffff 512GB user + ffffff8000000000 ffffffbfffffffff 256GB kernel logical memory map + [ffffffb000000000 ffffffbfffffffff] 64GB [kasan shadow region] + ffffffc000000000 ffffffc007ffffff 128MB bpf jit region + ffffffc008000000 ffffffc00fffffff 128MB modules + ffffffc010000000 fffffffdefffffff 253440MB vmalloc + fffffffdf0000000 fffffffdfdffffff 224MB fixed mappings (top down) + fffffffdfe000000 fffffffdfe7fffff 8MB [guard region]
Quoted 8 lines
Documentation/arm64/memory.rst The swapper_pg_dir address is written to TTBR1 and never written to · line 43
Quoted 4 lines
Documentation/arm64/memory.rst +4
-0+ fffffffdfe800000 fffffffdff7fffff 16MB PCI I/O space + fffffffdff800000 fffffffdffffffff 8MB [guard region] + fffffffe00000000 ffffffffefffffff 4GB vmemmap + ffffffff00000000 ffffffffffffffff 4GB [guard region]I wouldn't bother maintaining these. There are other combinations that people may use. The 4KB + 48-bit VA is defconfig while 64KB + 52-bit was more interesting, so we thought it would be useful.
If kernel config file isn't based on the defconfig, the 4KB + 39bit VA is the default option in Kconfig:
...
prompt "Page size"
default ARM64_4K_PAGES
help
Page size (translation granule) configuration.
...
choice
prompt "Virtual address space size"
default ARM64_VA_BITS_39 if ARM64_4K_PAGES
default ARM64_VA_BITS_47 if ARM64_16K_PAGES
default ARM64_VA_BITS_42 if ARM64_64K_PAGES
help
Allows choosing one of multiple possible virtual addressI believe this combination is widely used if 48bit VA isn't necessary. In fact, I think the default android GKI image is built with 4KB + 39bit VA. This is the reason why I added description for 4K + VA39 but leave other combinations.
Quoted 4 lines
I'm more inclined to remove them altogether and maybe just add some high-level ascii art as per the log of commit
f4693c2716b3("arm64: mm:
extend linear region for 52-bit VA configurations").
The detailed memory layout is useful, for example, I can immediately know which region the virtual address belongs to when checking kernel panic logs. If changed to high level ascii, I need to do some calculation, sometimes I need to check source code to get the value of some MACROS defitions.