MMU issues are some of the most frustrating to debug. To make this slightly less unbearable, introduce a software pagetable walker for ARMv8. This can be called to dump a pagetable with the default formatter, or a custom callback can be provided to implement more complicated parsing.
This can also be useful to dump the pagetable used by a previous bootloader stage (by reading out the ttbr register).
Here is an example of the output when walking U-Boot's own memory map on a Qualcomm RB3 board:
Walking pagetable at 000000017df90000, va_bits: 36. Using 3 levels [0x17df91000] | Table | | [0x17df92000] | Table | | [0x000001000 - 0x000200000] | Pages | Device-nGnRnE | Non-shareable [0x000200000 - 0x040000000] | Block | Device-nGnRnE | Non-shareable [0x040000000 - 0x080000000] | Block | Device-nGnRnE | Non-shareable [0x080000000 - 0x140000000] | Block | Normal | Inner-shareable [0x17df93000] | Table | | [0x140000000 - 0x17de00000] | Block | Normal | Inner-shareable [0x17df94000] | Table | | [0x17de00000 - 0x17dfa0000] | Pages | Normal | Inner-shareable
--- Changes in v2: - Document the MMU debugging features in doc/arch/arm64.rst - Mention that functions are stripped out when unused. - Link to v1: https://lore.kernel.org/r/20240607-caleb-upstreaming-v1-0-99094dabb3d9@linar...
--- Caleb Connolly (3): arm64: mmu.h: fix PTE_TABLE_AP arm64: add software pagetable walker doc: arch: arm64: describe pagetable debugging
arch/arm/cpu/armv8/cache_v8.c | 202 +++++++++++++++++++++++++++++++++++++++ arch/arm/include/asm/armv8/mmu.h | 57 ++++++++++- doc/arch/arm64.rst | 37 +++++++ 3 files changed, 295 insertions(+), 1 deletion(-) --- change-id: 20240607-caleb-upstreaming-82744a2786b3 base-commit: 22ca7e13dc02be83c29450ae4444add8e150ebdd
// Caleb (they/them)