Re: Nick's core remove PageReserved broke vmware...

[Hugh Dickins <hugh@veritas.com>]

On Thu, 3 Nov 2005, Michael S. Tsirkin wrote:
> All existing drivers that set VM_DONTCOPY also set VM_IO.
> So lets just disable playing with these flags from madvise if VM_IO is set.
> There's no reason I can see that the driver should have a say
> on what the process does with its own (non-IO) memory.
> Sounds good?

You're then saying that a process cannot set VM_DONTCOPY on a VM_IO
area to prevent the first child getting the area, but clear it after
so the next child does get a copy of the area.  I think it'd be wrong
(surprising) to limit the functionality in that way.

> By the way, as a separate issue, we still have a problem with DMA to pages
> which are *needed* by the child process. What do you think about VM_COPY
> (to do the old unix thing of actually copying the page instead of
> setting the COW flag) and a matching madvise call to set/clear it?

I don't much want to add another path into copy_pte_range, actually
copying pages.  If the process really wants DMA into such areas,
then it should contain the code for the child to COW them itself?

Hugh