From 42014ca5c0cb33693501ce2a18e4c1ceb536eede Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 25 Aug 2020 11:23:41 +0800 Subject: [PATCH] arm64: mm: define NET_IP_ALIGN to 0 mainline inclusion from mainline-v4.20-rc2 commit 26a4676faa1ad5d99317e0cd701e5d6f3e716b77 category: feature bugzilla: NA CVE: NA --------------------------- On arm64, there is no need to add 2 bytes of padding to the start of each network buffer just to make the IP header appear 32-bit aligned. Since this might actually adversely affect DMA performance some platforms, let's override NET_IP_ALIGN to 0 to get rid of this padding. Acked-by: Ilias Apalodimas Tested-by: Ilias Apalodimas Acked-by: Mark Rutland Acked-by: Will Deacon Signed-off-by: Ard Biesheuvel Signed-off-by: Catalin Marinas Signed-off-by: Hanjun Guo Signed-off-by: Yang Yingliang Reviewed-by: Xie XiuQi Signed-off-by: Yang Yingliang --- arch/arm64/include/asm/processor.h | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 98529c8b5d31..7695a5117ff2 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -24,6 +24,14 @@ #define KERNEL_DS UL(-1) #define USER_DS (TASK_SIZE_64 - 1) +/* + * On arm64 systems, unaligned accesses by the CPU are cheap, and so there is + * no point in shifting all network buffers by 2 bytes just to make some IP + * header fields appear aligned in memory, potentially sacrificing some DMA + * performance on some platforms. + */ +#define NET_IP_ALIGN 0 + #ifndef __ASSEMBLY__ /* -- GitLab