From 9c48c0965b97e14ddcf75490a754e84e05aaa062 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Oct 2017 12:12:16 +0200 Subject: [PATCH] x86/idt: Initialize early IDT before cr4_init_shadow() Moving the early IDT setup out of assembly code breaks the boot on first generation 486 systems. The reason is that the call of idt_setup_early_handler, which sets up the early handlers was added after the call to cr4_init_shadow(). cr4_init_shadow() tries to read CR4 which is not available on those systems. The accessor function uses a extable fixup to handle the resulting fault. As the IDT is not set up yet, the cr4 read exception causes an instantaneous reboot for obvious reasons. Call idt_setup_early_handler() before cr4_init_shadow() so IDT is set up before the first exception hits. Fixes: 87e81786b13b ("x86/idt: Move early IDT setup out of 32-bit asm") Reported-and-tested-by: Matthew Whitehead Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Andy Lutomirski Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1710161210290.1973@nanos --- arch/x86/kernel/head32.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c index cf2ce063f65a..2902ca4d5993 100644 --- a/arch/x86/kernel/head32.c +++ b/arch/x86/kernel/head32.c @@ -30,10 +30,11 @@ static void __init i386_default_early_setup(void) asmlinkage __visible void __init i386_start_kernel(void) { - cr4_init_shadow(); - + /* Make sure IDT is set up before any exception happens */ idt_setup_early_handler(); + cr4_init_shadow(); + sanitize_boot_params(&boot_params); x86_early_init_platform_quirks();