On Fri, 6 Dec 2013, Rik van Riel wrote: > > The basic race looks like this: > > CPU A CPU B CPU C > > load TLB entry > make entry PTE/PMD_NUMA > fault on entry > read/write old page > start migrating page
When you start migrating a page a special page migration entry is created that will trap all accesses to the page. You can safely flush when the migration entry is there. Only allow a new PTE/PMD to be put there *after* the tlb flush. > change PTE/PMD to new page Dont do that. We have migration entries for a reason. > read/write old page [*] Should cause a page fault which should put the process to sleep. Process will safely read the page after the migration entry is removed. > flush TLB Establish the new PTE/PMD after the flush removing the migration pte entry and thereby avoiding the race. > reload TLB from new entry > read/write new page > lose data > > [*] the old page may belong to a new user at this point! > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
