linux-kernel - Re: S4 resume broken since 2.6.39 (3.1, too)

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Date:	Thu, 22 Sep 2011 07:33:17 -0700
From:	Yinghai Lu <yinghai.lu@...cle.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Takashi Iwai <tiwai@...e.de>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>, oneukum@...e.de, x86@...nel.org,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: S4 resume broken since 2.6.39 (3.1, too)

On Wed, Sep 21, 2011 at 11:48 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> It looks like init_memory_mapping() is sometimes called with "end"
> beyond the last mapped PFN and it explodes when we try to write stuff to
> that address during image restoration.
>
> IOW, the Yinghai's assumption that init_memory_mapping() would always be
> called with a "good end" on x86_64 was overomptimistic.

for 64bit x86, kernel_physical_mapping_init() will use
map_low_page()/call early_memmap() to access ram for page_table that is above
rather last mapped PFN.

the point is:
on system with 64g, usable ram will be [0,2048m), [4g, 64g)
init_memory_mapping will be called two times for them.
before putting page_table high,
page table will be two parts: one is just below 512M, and one below 2048m.
after putting page_table high,
page table will be two parts: one is just below 2048M, and one below 64G.

one of the purposes is finding biggest continuous big range under
1024m for kdump.

Thanks

Yinghai
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