linux-kernel - Re: [tip:x86/urgent] x86, efi: Delete efi_ioremap() and fix CONFIG_X86

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Date:	Fri, 16 Mar 2012 12:01:40 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Matt Fleming <matt.fleming@...el.com>
Cc:	"H. Peter Anvin" <hpa@...nel.org>, mingo@...hat.com,
	mjg@...hat.com, linux-kernel@...r.kernel.org, keithp@...thp.com,
	rui.zhang@...el.com, huang.ying.caritas@...il.com,
	stable@...r.kernel.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86, efi: Delete efi_ioremap() and fix
 CONFIG_X86_32 oops

On Fri, Mar 16, 2012 at 11:36 AM, Matt Fleming <matt.fleming@...el.com> wrote:
> On Thu, 2012-03-15 at 10:54 -0700, Yinghai Lu wrote:
>> >                if (end <= max_low_pfn << PAGE_SHIFT)
>> >                        max_low_pfn_mapped = last_pfn_mapped;
>>
>> why max_low_pfn is used here?
>
> The idea is that we only want to update max_low_pfn_mapped when we've
> mapped a region at or below max_low_pfn. This maintains compatibility
> with behaviour prior to this patch.
>
>> > The max_low_pfn checks are only for CONFIG_X86_32 so that the behaviour
>> > is the same as before this patch, i.e. we don't try to map above
>> > max_low_pfn.
>>
>> ok, to simplify the code, in setup.c you could move
>> #ifdef CONFIG_X86_64
>>         if (max_pfn > max_low_pfn) {
>>                 /* can we preseve max_low_pfn ?*/
>>                 max_low_pfn = max_pfn;
>>         }
>> #endif
>>
>> before calling new init_memory_mapping()...
>>
>> so you could remove the #idef. in init_memory_mapping.
>
> Hmm.. if we do this then max_low_pfn_mapped will be set to max_pfn on
> CONFIG_X86_64 by the time we've finished looping in
> init_memory_mapping(). This is not how things work currently. Will that
> cause a problem?

oh, before this patch could be applied, you need to make sure all
max_low_pfn_mapped reference
is removed.
current assumption is under max_low_pfn_mapped all mem is mapped.
now with this patch, that assumption is not right anymore.

Yinghai
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