Messages in this thread | | | Date | Sun, 16 Aug 2009 09:04:51 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] kmemleak: Ignore the aperture memory hole on x86_64 |
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* Catalin Marinas <catalin.marinas@arm.com> wrote:
> On Sat, 2009-08-15 at 15:17 +0100, Ingo Molnar wrote: > > * Catalin Marinas <catalin.marinas@arm.com> wrote: > > > + /* > > > + * Kmemleak should not scan this block as it may not be mapped via the > > > + * kernel direct mapping. > > > + */ > > > + kmemleak_ignore(p); > > > > More importantly, kmemleak should _never_ do the garbage collection > > scan for device memory (such as the agp aperture above). All the > > aperture areas are in that category - PCI aperture, IOMMU areas, > > etc. etc. > > > > Please double check that kmemleak does not check those - there are > > devices where pure reading of that address space can have > > side-effects. > > I'll do a grep. But would such memory still be mapped in the > kernel direct mapping? [...]
It should not be mapped directly - we try to map all kinds of resources 'precisely', so that there can be no cache aliasing complications due to over-mapping - but still, there are compatibility ranges that are always mapped (the BIOS area for example).
> [...] In this particular case, it was alloc_bootmem() memory which > seems to have been unmapped (and cause an oops), otherwise, at > least on some architectures, may have problems with speculative > fetches. > > Kmemleak doesn't track other mappings like ioremap, so it should > not scan device memory. > > Since you raised this, I realised there is a class of kmalloc'ed > memory blocks that may have some issues on non-coherent > architectures. If such blocks are used for DMA and cache > invalidation is only done in dma_map_single(FROM_DEVICE) (the ARM > case), kmemleak scanning before dma_unmap_single() may pollute the > cache. One solution is to invalidate the caches again in > dma_unmap_single(). I'm not sure ignoring GFP_DMA blocks would be > feasible if this flag is used for other blocks containing > pointers. I need to do some tests but I don't think x86 is > affected.
Yeah, x86 shouldnt be affected.
Ingo
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