On Thu, 19 Oct 2006 00:00:27 -0700 (PDT)
David Miller <[email protected]> wrote:
> > > 1452 if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
> > > 1453 memset(kaddr, 0, PAGE_SIZE);
> > > 1454 kunmap_atomic(kaddr, KM_USER0);
> > > #### D-cache have to be flushed here.
> > > #### It seems it is just forgotten.
> > >
> > > 1455 return;
> > > 1456
> > > 1457 }
> > > 1458 copy_user_highpage(dst, src, va);
> > > #### Ok here. flush_dcache_page() called from this func if arch need it
> > > 1459 }
> > >
> >
> > This page has just been allocated and is private to the caller - there can
> > be no userspace mappings of it.
>
> Unfortunately, the kernel has just touched the page and thus there are
> active cache lines for the kernel side mapping. When we map this into
> user space, userspace might see stale cachelines instead of the
> memset() stores.
hm. Has it always been that way or did something change?
> Architectures typically take care of this in copy_user_page() and
> clear_user_page(). The absolutely depend upon those two routines
> being used for anonymous pages, and handle the D-cache issues there.
Only anonymous pages? There are zillions of places where we modify
pagecache without a flush, especially against the blockdev mapping (fs
metadata).
> But this code is going outside of that scope, and therefore needs
> an explicit D-cache flush.
OK, I'll add the patch.
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