forked from Minki/linux
d506a77251
The current get_unmapped_area code calls the f_ops->get_unmapped_area or the arch one (via the mm) only when MAP_FIXED is not passed. That makes it impossible for archs to impose proper constraints on regions of the virtual address space. To work around that, get_unmapped_area() then calls some hugetlbfs specific hacks. This cause several problems, among others: - It makes it impossible for a driver or filesystem to do the same thing that hugetlbfs does (for example, to allow a driver to use larger page sizes to map external hardware) if that requires applying a constraint on the addresses (constraining that mapping in certain regions and other mappings out of those regions). - Some archs like arm, mips, sparc, sparc64, sh and sh64 already want MAP_FIXED to be passed down in order to deal with aliasing issues. The code is there to handle it... but is never called. This series of patches moves the logic to handle MAP_FIXED down to the various arch/driver get_unmapped_area() implementations, and then changes the generic code to always call them. The hugetlbfs hacks then disappear from the generic code. Since I need to do some special 64K pages mappings for SPEs on cell, I need to work around the first problem at least. I have further patches thus implementing a "slices" layer that handles multiple page sizes through slices of the address space for use by hugetlbfs, the SPE code, and possibly others, but it requires that serie of patches first/ There is still a potential (but not practical) issue due to the fact that filesystems/drivers implemeting g_u_a will effectively bypass all arch checks. This is not an issue in practice as the only filesystems/drivers using that hook are doing so for arch specific purposes in the first place. There is also a problem with mremap that will completely bypass all arch checks. I'll try to address that separately, I'm not 100% certain yet how, possibly by making it not work when the vma has a file whose f_ops has a get_unmapped_area callback, and by making it use is_hugepage_only_range() before expanding into a new area. Also, I want to turn is_hugepage_only_range() into a more generic is_normal_page_range() as that's really what it will end up meaning when used in stack grow, brk grow and mremap. None of the above "issues" however are introduced by this patch, they are already there, so I think the patch can go ini for 2.6.22. This patch: Handle MAP_FIXED in powerpc's arch_get_unmapped_area() in all 3 implementations of it. Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Acked-by: William Irwin <bill.irwin@oracle.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Russell King <rmk+kernel@arm.linux.org.uk> Cc: David Howells <dhowells@redhat.com> Cc: Andi Kleen <ak@suse.de> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Kyle McMartin <kyle@mcmartin.ca> Cc: Grant Grundler <grundler@parisc-linux.org> Cc: Matthew Wilcox <willy@debian.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Adam Litke <agl@us.ibm.com> Cc: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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