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The mapping of the kernel consist of four segments, each of which is mapped with different permission attributes and/or lifetimes. To optimize the TLB and translation table footprint, we define various opaque constants in the linker script that resolve to different aligment values depending on the page size and whether CONFIG_DEBUG_ALIGN_RODATA is set. Considering that - a 4 KB granule kernel benefits from a 64 KB segment alignment (due to the fact that it allows the use of the contiguous bit), - the minimum alignment of the .data segment is THREAD_SIZE already, not PAGE_SIZE (i.e., we already have padding between _data and the start of the .data payload in many cases), - 2 MB is a suitable alignment value on all granule sizes, either for mapping directly (level 2 on 4 KB), or via the contiguous bit (level 3 on 16 KB and 64 KB), - anything beyond 2 MB exceeds the minimum alignment mandated by the boot protocol, and can only be mapped efficiently if the physical alignment happens to be the same, we can simplify this by standardizing on 64 KB (or 2 MB) explicitly, i.e., regardless of granule size, all segments are aligned either to 64 KB, or to 2 MB if CONFIG_DEBUG_ALIGN_RODATA=y. This also means we can drop the Kconfig dependency of CONFIG_DEBUG_ALIGN_RODATA on CONFIG_ARM64_4K_PAGES. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> |
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| .. | ||
| boot | ||
| configs | ||
| crypto | ||
| include | ||
| kernel | ||
| kvm | ||
| lib | ||
| mm | ||
| net | ||
| xen | ||
| Kconfig | ||
| Kconfig.debug | ||
| Kconfig.platforms | ||
| Makefile | ||