Messages in this thread | | | Subject | Re: [patch -mm series] ia64 specific /dev/mem handlers | From | Jes Sorensen <> | Date | 22 Feb 2005 09:41:04 -0500 |
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>>>>> "Andrew" == Andrew Morton <akpm@osdl.org> writes:
Andrew> jes@trained-monkey.org (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
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