From 6a50a664ca0cfd2a487525f10cec3ff4d570b5e8 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Wed, 2 May 2007 19:27:08 +0200 Subject: [PATCH] x86-64: build-time checking o X86_64 kernel should run from 2MB aligned address for two reasons. - Performance. - For relocatable kernels, page tables are updated based on difference between compile time address and load time physical address. This difference should be multiple of 2MB as kernel text and data is mapped using 2MB pages and PMD should be pointing to a 2MB aligned address. Life is simpler if both compile time and load time kernel addresses are 2MB aligned. o Flag the error at compile time if one is trying to build a kernel which does not meet alignment restrictions. Signed-off-by: Vivek Goyal Signed-off-by: Andi Kleen Cc: "Eric W. Biederman" Cc: Andi Kleen Signed-off-by: Andrew Morton --- arch/x86_64/kernel/head64.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'arch/x86_64/kernel') diff --git a/arch/x86_64/kernel/head64.c b/arch/x86_64/kernel/head64.c index 6c34bdd22e2..213d90e0475 100644 --- a/arch/x86_64/kernel/head64.c +++ b/arch/x86_64/kernel/head64.c @@ -62,6 +62,13 @@ void __init x86_64_start_kernel(char * real_mode_data) { int i; + /* + * Make sure kernel is aligned to 2MB address. Catching it at compile + * time is better. Change your config file and compile the kernel + * for a 2MB aligned address (CONFIG_PHYSICAL_START) + */ + BUILD_BUG_ON(CONFIG_PHYSICAL_START & (__KERNEL_ALIGN - 1)); + /* clear bss before set_intr_gate with early_idt_handler */ clear_bss(); -- cgit v1.2.3