Commit-ID: 9c48c0965b97e14ddcf75490a754e84e05aaa062
Gitweb: https://git.kernel.org/tip/9c48c0965b97e14ddcf75490a754e84e05aaa062
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Mon, 16 Oct 2017 12:12:16 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Mon, 16 Oct 2017 20:47:37 +0200
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 <whiteheadm@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
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 cf2ce06..2902ca4 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();
--
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