>>>>> "Andrew" == Andrew Morton <[EMAIL PROTECTED]> writes:
Andrew> [EMAIL PROTECTED] (Jes Sorensen) wrote: >> Hi, >> >> This patch introduces ia64 specific read/write handlers for >> /dev/mem access which is needed to avoid uncached pages to be >> accessed through the cached kernel window which can lead to random >> corruption. It also introduces a new page-flag PG_uncached which >> will be used to mark the uncached pages. I assume this may be >> useful to other architectures as well where the CPU may use >> speculative reads which conflict with uncached access. In addition >> I moved do_write_mem to be under ARCH_HAS_DEV_MEM as it's only ever >> used if that is defined. Andrew> Is it possible to avoid consuming a page flag? Andrew> If this is an ia64-only (or 64-bit-only) thing I guess we Andrew> could use bit 32. Hi Andrew, I don't think we can get away with it, I think most modern architectures have this problem. I've been trying to avoid it for several iterations but I kept getting pushed towards this. >> + if (page->flags & PG_uncached) Andrew> dude. That ain't gonna work ;) Pardon my lack of clue, but why not? Maybe I should explain how I use it - in the mspec driver I pull a chunk of pages out using alloc_pages and convert them all to uncached (I need to do a chunk due to the speculation restrictions on ia64) and then stick them into a special allocator and set page->PG_uncached when doing so (the allocator is not tied to the uncached so I posted the patch to Tony Luck). Ie. once the pages have been grabbed with alloc_pages() and converted to uncached, they are never put back into the generic pool. It may be there are other places which needs to learn to respect the flag? Cheers, Jes - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/