Re: BIOS overwritten during resume (was: Re: Asus L5D resume on battery power)

[Rafael J. Wysocki]

Hi,

On Wednesday, 2 of March 2005 23:05, Pavel Machek wrote:
> Hi!
> 
[-- snip --] 
> > It seems that we write to the BIOS while moving the image, at least on my box,
> > which is quite not correct, IMO.
[-- snip --]
> > 
> > IMO this may lead to unexpected results, like the mysterious reboots during
> > resume.
> 
> Well, I always thought that ROM-BIOS is expected to
> be... well... read-only? Can you really write to your BIOS? [I know
> about Flash-BIOSen, but they are certainly not writable by "normal"
> write.] Plus we should overwrite it with same values...
> 
> Anyway, IMO bios should be marked as reserved (and we should not be
> touching reserved pages). Can you verify that your BIOS is properly
> marked reserved? [Ccing l-k, this might be interesting.]

It is, but that's even more interesting.  Namely, the BIOS-e820 memory map
looks as follows:

BIOS-provided physical RAM map:
 BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
 BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
 BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
 BIOS-e820: 0000000000100000 - 000000001ff40000 (usable)
 BIOS-e820: 000000001ff40000 - 000000001ff50000 (ACPI data)
 BIOS-e820: 000000001ff50000 - 0000000020000000 (ACPI NVS)
 BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved)
 BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)

and the pages in the first two reserved areas are properly marked as reserved.
Moreover, there is an apparent hole between a0000 and e0000 which also
is marked as reserved.  However, we treat all of these pages as saveable
(a page is treated as non-saveable if it is marked as reserved _and_ satisfies
specific condition which is met by only one page on my system).  Consequently,
during resume we try to overwrite all of these pages and we not only try to
write to (theoretically) read-only areas, but also we try to write to where there's
nothing. :-)

Still, there are almost 3500 reserved pages on my system and I'm not sure that
we don't need to save at least some of them.  Anyway, I'm attaching the full
list of pages that are marked as reserved and treated as saveable, so they get
overwritten during resume.  Please have a look (these are virtual x86-64
addresses, but the mapping is straightforward).

Greets,
Rafael


-- 
- Would you tell me, please, which way I ought to go from here?
- That depends a good deal on where you want to get to.
		-- Lewis Carroll "Alice's Adventures in Wonderland"

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