Messages in this thread | | | Date | Wed, 04 Jul 2007 16:31:06 +1000 | From | Nick Piggin <> | Subject | Re: [BUGFIX][PATCH] DO flush icache before set_pte() on ia64. |
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KAMEZAWA Hiroyuki wrote: > This is a experimental patch for fixing icache flush race of ia64(Montecito). > > Problem Description: > Montecito, new ia64 processor, has separated L2 i-cache and d-cache, > and i-cache and d-cache is not consistent in automatic way. > > L1 cache is also separated but L1 D-cache is write-through. Then, before > Montecito, any changes in L1-dcache is visible in L2-mixed-cache consistently. > > Montecito has separated L2 cache and Mixed L3 cache. But...L2 D-cache is > *write back*. (See http://download.intel.com/design/Itanium2/manuals/ > 30806501.pdf section 2.3.3) > > Assume : valid data is in L2 d-cache and old data in L3 mixed cache. > If write-back L2->L3 is delayed, at L2 i-cache miss cpu will fetch old data > in L3 mixed cache. > By this, L2-icache-miss will read wrong instruction from L3-mixed cache. > (Just I think so, is this correct ?) > > Anyway, there is SIGILL problem in NFS/ia64 and icache flush can fix > SIGILL problem (in our HPC team test.) > > Following SIGILL issue occurs in current kernel. > (This was a discussion in this April) > - http://www.gelato.unsw.edu.au/archives/linux-ia64/0704/20323.html > Usual file systems uses DMA and it purges cache. But NFS uses copy-by-cpu. > > This is HP-UX's errata comment: > - http://h50221.www5.hp.com/upassist/itrc_japan/assist2/patchdigest/PHKL_36120.html > (Sorry for Japanese page...but English comments also written. See PHKL_36120) > > Now, I think icache should be flushed before set_pte(). > This is a patch to try that. > > 1. remove all lazy_mmu_prot_update()...which is used by only ia64. > 2. implements flush_cache_page()/flush_icache_page() for ia64. > > Something unsure.... > 3. mprotect() flushes cache before removing pte. Is this sane ? > I added flush_icache_range() before set_pte() here. > > Any comments and advices ?
Thanks, this is the way I wanted to see it go in the generic code. (ie. get rid of lazy_mmu_prot_uptdate and actually follow the cacheflush API instead).
The only thing I noticed when I looked at the code is that some places may not have flushed icache when they should have? Did you get them all? Minor nitpick: you have one place where you test VM_EXEC before flushing, but the flush routine itself contains the same test I think?
Regarding the ia64 code -- I'm not an expert so I can't say whether it is the right thing to do or not. However I still can't work out what it's rationale for the PG_arch_1 bit is, exactly. Does it assume that flush_dcache_page sites would only ever be encountered by pages that are not faulted in? A faulted in page kind of is "special" because it is guaranteed uptodate, but is the ia64 arch code relying on that? Should it? (there could definitely still be flush_dcache_page called on mapped pages, but it should only be a subset of all possible sites -- I don't know if it is too clean for ia64 cacheflush code to know that?). [*]
[*] all this is, as usual, predicated by the disclaimer that quirks in mm/ can result in mapped pages not being uptodate (in which case hell often breaks loose in other ways anyway).
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