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x86/idt: Initialize early IDT before cr4_init_shadow()

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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: 87e81786b1 ("x86/idt: Move early IDT setup out of 32-bit asm")
Reported-and-tested-by:  Matthew Whitehead <whiteheadm@acm.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1710161210290.1973@nanos
This commit is contained in:
Thomas Gleixner 2017-10-16 12:12:16 +02:00
parent e6fc454b77
commit 9c48c0965b
1 changed files with 3 additions and 2 deletions
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5
arch/x86/kernel/head32.c
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@ -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();