Commit e16e65a0 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Catalin Marinas
Browse files

arm64: remove CONFIG_DEBUG_ALIGN_RODATA feature 



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: default avatarArd Biesheuvel <ardb@kernel.org>
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Acked-by: default avatarWill Deacon <will@kernel.org>
Acked-by: default avatarLaura Abbott <labbott@kernel.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent b8fdef31

arch/arm64/Kconfig.debug

+0 −13
Original line number Diff line number Diff line
@@ -52,19 +52,6 @@ config DEBUG_WX 


	  If in doubt, say "Y".



config DEBUG_ALIGN_RODATA

	depends on STRICT_KERNEL_RWX

	bool "Align linker sections up to SECTION_SIZE"

	help

	  If this option is enabled, sections that may potentially be marked as

	  read only or non-executable will be aligned up to the section size of

	  the kernel. This prevents sections from being split into pages and

	  avoids a potential TLB penalty. The downside is an increase in

	  alignment and potentially wasted space. Turn on this option if

	  performance is more important than memory pressure.



	  If in doubt, say N.



config DEBUG_EFI

	depends on EFI && DEBUG_INFO

	bool "UEFI debugging"

arch/arm64/include/asm/memory.h

+1 −11
Original line number Diff line number Diff line
@@ -120,22 +120,12 @@ 


/*

 * Alignment of kernel segments (e.g. .text, .data).

 */

#if defined(CONFIG_DEBUG_ALIGN_RODATA)

/*

 *  4 KB granule:   1 level 2 entry

 * 16 KB granule: 128 level 3 entries, with contiguous bit

 * 64 KB granule:  32 level 3 entries, with contiguous bit

 */

#define SEGMENT_ALIGN		SZ_2M

#else

/*

 *

 *  4 KB granule:  16 level 3 entries, with contiguous bit

 * 16 KB granule:   4 level 3 entries, without contiguous bit

 * 64 KB granule:   1 level 3 entry

 */

#define SEGMENT_ALIGN		SZ_64K

#endif



/*

 * Memory types available.

drivers/firmware/efi/libstub/arm64-stub.c

+3 −5
Original line number Diff line number Diff line
@@ -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

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