RE: [git pull] x86 PAT changes

Linus Torvalds
2008-04-26T17:16:17Z

On Sat, 26 Apr 2008, Pallipadi, Venkatesh wrote:
>
> Agreed that NONPROMISC_DEVMEM is not really needed for read/write. But,
> we will still need it for /dev/mem.

If so, just disable it unconditionally for mmap.

As mentioned, that's really just a return to original Linux /dev/mmap
semantics: long ago (well, not _that_ long ago) we never used to be able
to mmap() normal kernel memory, because the page counts would get screwed
up on pages that weren't marked PG_Reserved.

So the traditional Linux behavior for mmap() on /dev/mem was always to
only allow it on memory that either had no "struct page *" backing at all,
or that was marked PG_Reserved (ie the ISA hole ay 640k-1M and things like
the BIOS tables etc).

Going back to that doesn't sound horrible.

Linus