linux-kernel - Re: linux-next: reservetop fix disables mem=

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Date:	Sat, 19 Sep 2009 11:02:10 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zachary Amsden <zach@...are.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Xiao Guangrong <xiaooguangrong@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: linux-next: reservetop fix disables mem=

Ingo Molnar wrote:
> I thoroughly zapped it. Do you know about any commit ID where it snuck 
> in?

after close looking, it will break
1. some cpu feature  in early stage too, like cpu_has_x2apic
2. will break built-in-command line
3. will break other memmap= and mem=
4. early_dbgp and early_console that will use early_ioremap to access mmio (?)

YH

commit 8126dec32738421afa362114337331337b4be17f
Author: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Date:   Thu Aug 20 20:23:11 2009 +0800

    x86: Fix system crash when loading with "reservetop" parameter
    
    The system will die if the kernel is booted with "reservetop"
    parameter, in present code, parse "reservetop" parameter after
    early_ioremap_init(), and some function still use
    early_ioremap() after it.
    
    The problem is, "reservetop" parameter can modify
    'FIXADDR_TOP', then the virtual address got by early_ioremap()
    is base on old 'FIXADDR_TOP', but the page mapping is base on
    new 'FIXADDR_TOP', it will occur page fault, and the IDT is not
    prepare yet, so, the system is dead.
    
    So, put parse_early_param() in the front of
    early_ioremap_init() in this patch.
    
    Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
    Cc: yinghai@...nel.org
    Cc: Andrew Morton <akpm@...ux-foundation.org>
    LKML-Reference: <4A8D402F.4080805@...fujitsu.com>
    Signed-off-by: Ingo Molnar <mingo@...e.hu>

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 63f32d2..02643cc 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -711,6 +711,11 @@ void __init setup_arch(char **cmdline_p)
        printk(KERN_INFO "Command line: %s\n", boot_command_line);
 #endif
 
+       strlcpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
+       *cmdline_p = command_line;
+
+       parse_early_param();
+
        /* VMI may relocate the fixmap; do this before touching ioremap area */
        vmi_init();
 
@@ -793,11 +798,6 @@ void __init setup_arch(char **cmdline_p)
 #endif
 #endif
 
-       strlcpy(command_line, boot_command_line, COMMAND_LINE_SIZE);
-       *cmdline_p = command_line;
-
-       parse_early_param();
-
 #ifdef CONFIG_X86_64
        check_efer();
 #endif


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