From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Thu, 3 Mar 2016 14:09:41 +0100 Subject: [PATCH 3/3] arm64: simplify kernel segment mapping granularity In-Reply-To: <1457010581-4924-1-git-send-email-ard.biesheuvel@linaro.org> References: <1457010581-4924-1-git-send-email-ard.biesheuvel@linaro.org> Message-ID: <1457010581-4924-4-git-send-email-ard.biesheuvel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. Signed-off-by: Ard Biesheuvel --- arch/arm64/kernel/vmlinux.lds.S | 25 ++++++++++++-------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 7a141c098bbb..2c60d19b038c 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -63,14 +63,19 @@ PECOFF_FILE_ALIGNMENT = 0x200; #endif #if defined(CONFIG_DEBUG_ALIGN_RODATA) -#define ALIGN_DEBUG_RO . = ALIGN(1<