Date: Thu, 8 Apr 2010 09:05:58 +0800
From: Liang Li <liang.li@windriver.com>
To: Yinghai <yinghai.lu@oracle.com>
Cc: akpm@linux-foundation.org, hpa@zytor.com, mingo@elte.hu,
       tglx@linutronix.de, wangchen@cn.fujitsu.com,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: + x86-fix-handling-of-the-reservetop-boot-option.patch added to
 -mm tree
Message-ID: <20100408010558.GA4053@localhost>
Reply-To: Liang Li <liang.li@windriver.com>
References: <201004072200.o37M0d19009878@imap1.linux-foundation.org>
 <4BBD1AA3.4000204@oracle.com>
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On Wed, Apr 07, 2010 at 04:52:03PM -0700, Yinghai wrote:
> On 04/07/2010 03:00 PM, akpm@linux-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@windriver.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@windriver.com>
> > Cc: Wang Chen <wangchen@cn.fujitsu.com>
> > Cc: Ingo Molnar <mingo@elte.hu>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: Yinghai Lu <yinghai@kernel.org>
> > Signed-off-by: Andrew Morton <akpm@linux-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.

#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.

Thanks and best regards,
		-Liang Li
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