Messages in this thread | | | Date | Mon, 11 Aug 2008 12:09:08 -0700 | From | Suresh Siddha <> | Subject | Re: [rfc][patch] x86: avoid highmem cache attribute aliasing |
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On Mon, Aug 11, 2008 at 10:10:19AM -0700, Ingo Molnar wrote: > > * Nick Piggin <npiggin@suse.de> wrote: > > > Highmem code can leave ptes and tlb entries around for a given page > > even after kunmap, and after it has been freed. > > > > From what I can gather, the PAT code may change the cache attributes > > of arbitrary physical addresses (ie. including highmem pages), which > > would result in aliases in the case that it operates on one of these > > lazy tlb highmem pages. > > > > Flushing kmaps should solve the problem. > > > > I've also just added code for conditional flushing if we haven't got > > any dangling highmem aliases -- this should help performance if we > > change page attributes frequently or systems that aren't using much > > highmem pages (eg. if < 4G RAM). Should be turned into 2 patches, but > > just for RFC... > > hm, such aliasing might happen in theory - and i guess in practice too > if the AGP driver allocates/deallocates aperture in short succession. > > Maybe this could corrupt the X framebuffer - or even generic kernel RAM. > Mind resending the two split up patches? The fix we might want to take > into v2.6.27, the speedup probably for v2.6.28. > > But maybe i'm missing something obvious that prevents such problems on > 32-bit systems - Venki, Suresh, what do you think?
Andi pointed out in another thread that we don't use GFP_HIGHMEM in the AGP drivers. And hence we haven't encountered an issue so far. But yes, this is a good fix to close the hole.
thanks, suresh
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