Messages in this thread | | | Date | Thu, 19 Oct 2006 00:17:47 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] mm:D-cache aliasing issue in cow_user_page |
| |
On Thu, 19 Oct 2006 00:00:27 -0700 (PDT) David Miller <davem@davemloft.net> 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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |