RE: [patch 02/11] PAT x86: Map only usable memory in x86_64 identitymap and kernel text

[Linus Torvalds]

On Thu, 10 Jan 2008, Pallipadi, Venkatesh wrote:
> 
> Yes. I had those pages not mapped at all earlier. The reason I switched
> to zero page is to continue support cases like:
>  BIOS-e820: 0000000000000000 - 000000000009cc00 (usable)
>  BIOS-e820: 000000000009cc00 - 00000000000a0000 (reserved)
>  BIOS-e820: 00000000000cc000 - 00000000000d0000 (reserved)
>  BIOS-e820: 00000000000e4000 - 0000000000100000 (reserved)
>  BIOS-e820: 0000000000100000 - 00000000cff60000 (usable)
> 
> In this case if some one does a dd of /dev/mem before they can read the
> contents of usable memory in 0x100000-0xcff60000 range.

Well, I think that /dev/mem should simply give them the right info. That's 
what people use /dev/mem for - doing things like reading BIOS images etc. 

So returning *either* a zero page *or* stopping at the first hole is both 
equally wrong. 

			Linus
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