Re: 2.6.23: does it supposed to work on an i486?

["H. Peter Anvin" <hpa@zytor.com>]

Michael Tokarev wrote:
> I tried to upgrade one of our ooooold machines
> (used as print servers and similar tasks) today
> from 2.6.22 to 2.6.23[.9].  The same config (with
> minor tweaks for new options), i486 base arch,
> X86_GENERIC=y.
>
> The result is immediately machine reboot right
> after bootloader (etherboot) passes control to
> the kernel -- BEFORE "Uncompressing linux"
> message.
>
> 2.6.22 worked just fine.
>
> So I wonder if it's supposed to work in the first
> place.  The thing is that this machine(s) are very
> slow to boot, so trying to figure out which change
> is at question will require quite some time...

It looks like 2.6.23.9 is missing checkin 
7ed192906a2144ebc8ca2925a85d27b9c5355668 from Linus' tree (attached), 
which is necessary to work on 386 and 486.

	-hpa

>From 7ed192906a2144ebc8ca2925a85d27b9c5355668 Mon Sep 17 00:00:00 2001
From: H. Peter Anvin <hpa@zytor.com>
Date: Sun, 4 Nov 2007 17:50:12 -0800
Subject: [PATCH] x86 setup: add a near jump to serialize %cr0 on 386/486

The 386 and 486 needs a jump immediately after setting %cr0 in order
to serialize the pipeline.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---
 arch/x86/boot/pmjump.S |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/pmjump.S b/arch/x86/boot/pmjump.S
index 2e55923..26baeab 100644
--- a/arch/x86/boot/pmjump.S
+++ b/arch/x86/boot/pmjump.S
@@ -31,14 +31,14 @@ protected_mode_jump:
 	xorl	%ebx, %ebx		# Flag to indicate this is a boot
 	movl	%edx, %esi		# Pointer to boot_params table
 	movl	%eax, 2f		# Patch ljmpl instruction
-	jmp	1f			# Short jump to flush instruction q.
 
-1:
 	movw	$__BOOT_DS, %cx
 
 	movl	%cr0, %edx
 	orb	$1, %dl			# Protected mode (PE) bit
 	movl	%edx, %cr0
+	jmp	1f			# Short jump to serialize on 386/486
+1:
 
 	movw	%cx, %ds
 	movw	%cx, %es
-- 
1.5.3.4