On 05/14/2014 02:29 AM, Anthony Iliopoulos wrote: > The invalidation is required in order to maintain proper semantics > under CoW conditions. In scenarios where a process clones several > threads, a thread operating on a core whose DTLB entry for a > particular hugepage has not been invalidated, will be reading from > the hugepage that belongs to the forked child process, even after > hugetlb_cow(). > > The thread will not see the updated page as long as the stale DTLB > entry remains cached, the thread attempts to write into the page, > the child process exits, or the thread gets migrated to a different > processor. No to be too nitpicky, but this applies to ITLB too, right? I believe this bug came all the way back from: > commit 1e8f889b10d8d2223105719e36ce45688fedbd59 > Author: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> > Date: Fri Jan 6 00:10:44 2006 -0800 > > [PATCH] Hugetlb: Copy on Write support It was probably the first time that we ever changed an _existing_ hugetlbfs pte, and that patch probably just missed the TLB flush because none of the other pte-setting hugetlb.c code needed TLB flushes. The bogus x86 version of huge_ptep_clear_flush() came from the s390 guys, so double-shame on IBM! :P > commit 8fe627ec5b7c47b1654dff50536d9709863295a3 > Author: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> > Date: Mon Apr 28 02:13:28 2008 -0700 > > hugetlbfs: add missing TLB flush to hugetlb_cow() This is probably an opportunity for all the other architecture maintainers to make sure that they have proper copies of huge_ptep_clear_flush(). I went through the hugetlb code on x86 and couldn't find another TLB flush that fixes this issue, and I believe this is correct, so: Acked-by: Dave Hansen <dave.hansen@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
