Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: BIOS overwritten during resume (was: Re: Asus L5D resume on battery power) | Date | Thu, 3 Mar 2005 09:02:47 +0100 |
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Hi,
On Thursday, 3 of March 2005 00:54, Pavel Machek wrote: > Hi! > > > > > 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). > > [looking at code] > > IIRC kernel code/data is marked as PageReserved(), that's why we need > to save that :(. Not sure what to do with data e820 marked as > reserved...
Perhaps we need another page flag, like PG_readonly, and mark the pages reserved by the e820 as PG_reserved | PG_readonly (the same for the areas that are not returned by e820 at all). Would that be acceptable?
Greets, Rafael
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