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arm64: remove CONFIG_DEBUG_ALIGN_RODATA feature

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When CONFIG_DEBUG_ALIGN_RODATA is enabled, kernel segments mapped with
different permissions (r-x for .text, r-- for .rodata, rw- for .data,
etc) are rounded up to 2 MiB so they can be mapped more efficiently.
In particular, it permits the segments to be mapped using level 2
block entries when using 4k pages, which is expected to result in less
TLB pressure.

However, the mappings for the bulk of the kernel will use level 2
entries anyway, and the misaligned fringes are organized such that they
can take advantage of the contiguous bit, and use far fewer level 3
entries than would be needed otherwise.

This makes the value of this feature dubious at best, and since it is not
enabled in defconfig or in the distro configs, it does not appear to be
in wide use either. So let's just remove it.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Laura Abbott <labbott@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Ard Biesheuvel
2020-03-29 16:12:58 +02:00
committed by Catalin Marinas
parent b8fdef311a
commit e16e65a029
3 changed files with 4 additions and 29 deletions
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8
drivers/firmware/efi/libstub/arm64-stub.c
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@@ -82,14 +82,12 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && phys_seed != 0) {
/*
* If CONFIG_DEBUG_ALIGN_RODATA is not set, produce a
* displacement in the interval [0, MIN_KIMG_ALIGN) that
* doesn't violate this kernel's de-facto alignment
* Produce a displacement in the interval [0, MIN_KIMG_ALIGN)
* that doesn't violate this kernel's de-facto alignment
* constraints.
*/
u32 mask = (MIN_KIMG_ALIGN - 1) & ~(EFI_KIMG_ALIGN - 1);
u32 offset = !IS_ENABLED(CONFIG_DEBUG_ALIGN_RODATA) ?
(phys_seed >> 32) & mask : TEXT_OFFSET;
u32 offset = (phys_seed >> 32) & mask;
/*
* With CONFIG_RANDOMIZE_TEXT_OFFSET=y, TEXT_OFFSET may not