linux-kernel - Re: + x86-fix-handling-of-the-reservetop-boot-option.patch added to -mm tree

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Message-ID: <4BBD2DD4.1060101@oracle.com>
Date:	Wed, 07 Apr 2010 18:13:56 -0700
From:	Yinghai <yinghai.lu@...cle.com>
To:	Liang Li <liang.li@...driver.com>
CC:	akpm@...ux-foundation.org, hpa@...or.com, mingo@...e.hu,
	tglx@...utronix.de, wangchen@...fujitsu.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: + x86-fix-handling-of-the-reservetop-boot-option.patch added
 to -mm tree

On 04/07/2010 06:05 PM, Liang Li wrote:
> On Wed, Apr 07, 2010 at 04:52:03PM -0700, Yinghai wrote:
>> On 04/07/2010 03:00 PM, akpm@...ux-foundation.org wrote:
>>> The patch titled
>>>      x86: fix handling of the 'reservetop' boot option
>>> has been added to the -mm tree.  Its filename is
>>>      x86-fix-handling-of-the-reservetop-boot-option.patch
>>>
>>> Before you just go and hit "reply", please:
>>>    a) Consider who else should be cc'ed
>>>    b) Prefer to cc a suitable mailing list as well
>>>    c) Ideally: find the original patch on the mailing list and do a
>>>       reply-to-all to that, adding suitable additional cc's
>>>
>>> *** Remember to use Documentation/SubmitChecklist when testing your code ***
>>>
>>> See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
>>> out what to do about this
>>>
>>> The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
>>>
>>> ------------------------------------------------------
>>> Subject: x86: fix handling of the 'reservetop' boot option
>>> From: Liang Li <liang.li@...driver.com>
>>>
>>> When specifying the 'reservetop=0xbadc0de' kernel parameter, the kernel
>>> will stop booting due to a early_ioremap bug that relate to commit
>>> 8827247ff ("x86: don't define __this_fixmap_does_not_exist()").
>>>
>>> The root cause of boot failure problem is the value of 'slot_virt[i]' was
>>> initialized in setup_arch->early_ioremap_init.  But later in setup_arch,
>>> the function 'parse_early_param' will modify 'FIXADDR_TOP' when
>>> 'reservetop=0xbadc0de' being specified.
>>>
>>> The simplest fix might be use __fix_to_virt(idx0) to get updated value
>>> of 'FIXADDR_TOP' in '__early_ioremap' instead of reference old value
>>> from slot_virt[slot] directly.
>>>
>>> Signed-off-by: Liang Li <liang.li@...driver.com>
>>> Cc: Wang Chen <wangchen@...fujitsu.com>
>>> Cc: Ingo Molnar <mingo@...e.hu>
>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>> Cc: "H. Peter Anvin" <hpa@...or.com>
>>> Cc: Yinghai Lu <yinghai@...nel.org>
>>> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>>> ---
>>>
>>>  arch/x86/mm/ioremap.c |    4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff -puN arch/x86/mm/ioremap.c~x86-fix-handling-of-the-reservetop-boot-option arch/x86/mm/ioremap.c
>>> --- a/arch/x86/mm/ioremap.c~x86-fix-handling-of-the-reservetop-boot-option
>>> +++ a/arch/x86/mm/ioremap.c
>>> @@ -537,9 +537,9 @@ __early_ioremap(resource_size_t phys_add
>>>  		--nrpages;
>>>  	}
>>>  	if (early_ioremap_debug)
>>> -		printk(KERN_CONT "%08lx + %08lx\n", offset, slot_virt[slot]);
>>> +		printk(KERN_CONT "%08lx + %08lx\n", offset, __fix_to_virt(idx0));
>>>  
>>> -	prev_map[slot] = (void __iomem *)(offset + slot_virt[slot]);
>>> +	prev_map[slot] = (void __iomem *)(offset + __fix_to_virt(idx0));
>>>  	return prev_map[slot];
>>>  }
>>>  
>>> _
>>
>> not that simple. but it looks like correct direction.
>>
>> please consider:
>> when early_parsing reserve_top, double check if there is left over in prev_map[], and 
>> reinitialize slot_virt[] and clear old PMD and  setup new PMD if needed.
> 
> Hi Yinghai,
> 
> Thanks for your reply, its better to have eyes on then being ignored. :)
> 
> Your suggestions were considered before the patch to public, let me try
> to explain:
> 
> #1 check/adjust prev_map[]?
> In my tests, seems early_ioremap is untouched between early_ioremap_init
> and parse_early_param so I did not check prev_map. Even its get touched,
> I think we could do nothing to this mapping, since prev_map[i] just
> record virt addr for clients of early_ioremap. We can check and adjust
> prev_map but clients of early_ioremap won't realize the fact so nothing
> being fixed or broken.

efi related code need them

dmi 

you need to add bug_on if there is still have left over, and need the caller to re map it again later.

> 
> #2 reinitialize slot_virt and update PMD
> I actually tried this approach, call early_ioremap_init again after
> parse_early_param will do that work, it also works but I am not sure
> that is the better solution or too heavy for solve the problem? So I
> tend to say 'simplest' solution in git commit log.

how about PMD? you don't need set PMD again.

YH
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