Re: [PATCH 10 of 20] ipath - support for userspace apps using core driver

[Hugh Dickins <hugh@veritas.com>]

On Thu, 16 Mar 2006, Nick Piggin wrote:
> > 
> > How about the case where one wants to map pages from
> > dma_alloc_coherent() into userspace?  It seems one should do
> > get_page() in .nopage, and then the driver can do dma_free_coherent()
> > when the vma is released.
> 
> I think so, provided you set VM_IO on the vma. You need VM_IO to
> ensure that get_user_pages callers can't hijack your page's lifetime
> rules

Once __GFP_COMP is passed to the dma_alloc_coherent, as it needs to be
(unless going VM_PFNMAP), get_user_pages will be safe: no need for VM_IO.

Hugh
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