"David S. Miller" <[email protected]> wrote:
>
> From: Andrew Morton <[email protected]>
> Date: Sun, 12 Feb 2006 18:13:12 -0800
>
> > We have a page which has no ->mapping, but lo, it's mmapped by userspace
> > and can be MAP_SHARED between different CPUs and processes.
> >
> > Yes, I suspect it'll do the wrong thing in unpleasantly subtle ways.
> >
> > (cc's davem and runs away).
>
> The ->mapping check is there essentially to hit user mapped pages that
> would be modified by the kernel using kernel space memory accesses
> other than those done by copy_user_page() and clear_user_page() (and
> their brothers copy_user_highpage() and clear_user_highpage() which
> just call the former directly on a non-HIGHPAGE platform like
> sparc64).
The direct-io.c code just does memset. (That's very common - maybe
clear_user_highpage_partial() is needed?)
> Hugepages actually have no D-cache aliasing issues by definition on
> sparc64 because the smallest possible hugepage size is 64K which is
> larger than the D-cache aliasing factor (which is 16K).
OK.. So it would be a bug, except for this hardware quirk. I'll check the
other architectures.
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