Messages in this thread | | | Date | Mon, 10 Nov 2003 18:17:37 +0100 | From | Manfred Spraul <> | Subject | Re: EFAULT reading /dev/mem... - broken x86info |
| |
Dave Jones wrote:
>On Mon, Nov 10, 2003 at 05:50:25PM +0100, Manfred Spraul wrote: > > It breaks either your app or your AGP driver - what's simpler to fix? > > I'm biased, because if you update the AGP driver, then I must figure out > > how to fix DEBUG_PAGEALLOC 8-) > >I'm not convinced changing agpgart is worth the pain. >The only userspace app that actually grovels through the aperture >in this way is the agpgart test code, so this shouldn't be an issue. > > You misunderstood my objection: we cannot assume that every page is mapped in the kernel linear mapping: - with DEBUG_PAGEALLOC, lots of pages are removed from the linear mapping - even without it, all pages that are used for AGP are removed from the mapping.
Thus if something fails with DEBUG_PAGEALLOC, it will fail sometimes with AGP gart as well.
>I thought the DEBUG_PAGEALLOC stuff just unmapped pages that had been >kmalloc'd ? The area of memory we're trying to read those mptables from >shouldn't be unmapped in the first place should they ? Confused. > > DEBUG_PAGEALLOC unmaps pages on kmem_cache_free and __free_pages(). The pages are mapped again during get_free_pages and kmem_cache_alloc.
0x86000 looks like a normal page - what guarantees that it's not used by the kernel?
-- Manfred
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |