Re: [PATCH][Fix] Fix Bug #4959 (take 2)

Pavel Machek
2005-09-27T18:41:12Z

Hi!

I do not really like new exports from swsusp.c, but I'm afraid
there's no way around.

> The following patch fixes Bug #4959. For this purpose it creates temporary
> page translation tables including the kernel mapping (reused) and the direct
> mapping (created from scratch) and makes swsusp switch to these tables
> right before the image is restored.

Why do you need *two* mappings? Should not just kernel mapping be enough?

> NOTES:
> (1) I'm quite sure that to fix the problem we need to use temporary page
> translation tables that won't be modified in the process of copying the image.
> (2) These page translation tables have to be present in memory before the
> image is copied, so there are two possible ways in which they can be created:
> (a) in the startup kernel code that is executed before calling swsusp
> on resume, in which case they have to be marked with PG_nosave,
> (b) in swsusp, after the image has been loaded from disk (to set up
> the tables we need to know which pages will be overwritten while
> copying the image).
> However, (a) is tricky, because it will only work if the tables are always located
> at the same physical addresses, which I think would be quite difficult to achieve.

Why? Reserve ten pages for them... static char resume_page_tables[10*PAGE_SIZE] does not
sound that bad.

> Moreover, such a code would have to be executed on every boot and the
> temporary page tables would always be present in memory.

Yep, but I do not see that as a big problem.

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