Re: How does the kernel map physical to virtual addresses?

From: Stephen C. Tweedie (
Date: Mon Aug 28 2000 - 10:12:52 EST


On Mon, Aug 28, 2000 at 01:56:34PM +0100, Tigran Aivazian wrote:
> it is interesting to observe that many questions that deal with _details_
> are answered quickly but questions related to fundamental concepts related
> to how Linux is designed, baffle all of us (since 0 people answered). So,
> is there really nobody in the whole world who can answer this? I would
> like to know the answer (about global kernel memory layout - i.e. what
> goes into PSE pages and what goes into normal ones, and how does PAE mode
> change the picture?) myself...

If PSE is available, it is used to map the bits of the kernel's
VA which permanently maps all of physical memory. As a result, those
pages cannot necessarily be looked up via a normal page table walk.
Anything dynamically mapped --- ie. high pages (if using PAE), or
vmalloc/ioremap pages --- is mapped using normal 4k ptes.

mem_map[] is completely unaffected by the use of PSE, and continues to
keep one entry per 4k physical page regardless of how the page tables
have been constructed.

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