Messages in this thread | | | Subject | Re: User switchable HW mappings & cie | From | Benjamin Herrenschmidt <> | Date | Mon, 09 Oct 2006 21:51:01 +1000 |
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> I'm very much for this approach, possibly with the extension that we > could have a multiple-page version as well, as populating the whole vma > sometimes may be cheaper than populating each pte with a fault. That > would basically be an io_remap_pfn_range() which is safe when the > mmap_sem is taken in read mode (from do_no_page). > > One problem that occurs is that the rule for ptes with non-backing > struct pages > Which I think was introduced in 2.6.16: > > pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT) > > cannot be honored, at least not with the DRM memory manager, since the > graphics object will be associated with a vma and not the underlying > physical address. User space will have vma->vm_pgoff as a handle to the > object, which may move around in graphics memory.
That's a problem with VM_PFNMAP set indeed. get_user_pages() is a non-issue with VM_IO set too but I'm not sure about other code path that might try to hit here... though I think we don't hit that if MAP_SHARED, Nick ?
Ben.
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