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SubjectRe: Access to non-RAM pages
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On Sun, 2018-09-02 at 18:38 -0700, Linus Torvalds wrote:
> On Sun, Sep 2, 2018 at 6:32 PM Benjamin Herrenschmidt
> <benh@kernel.crashing.org> wrote:
> >
> > Also, if we cross page boundaries with those guys then we have a bigger
> > problem no ? we could fall off a vmalloc page into the nether or into
> > an ioremap mapping no ?
>
> It's not used for vmalloc stuff. It's just regular kmalloc().
>
> So it can cross pages, and it can fall off the end of memory, but it
> can't do random stuff.

Ok, it might be worth adding a DEBUG_VM based (or similar) warning in
case somebody ever thinks of passing a vmalloc pointer to it...

As for falling out of the end of memory, yes it could be a real problem
though I don't see why IO is any different than just hitting a non-
mapped area in that regard. So we should probably keep an unused
(readonly if possible) zero page at the end.

Cheers,
Ben.

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