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authorJeremy Fitzhardinge <jeremy@goop.org>2009-02-04 18:33:38 -0800
committerH. Peter Anvin <hpa@zytor.com>2009-02-04 21:33:09 -0800
commitb534816b552d35bbd3c60702139ed5c7da2f55c2 (patch)
tree1e48095368b05b498264105757e6d79e78dace62 /Documentation
parent4560839939f4b4a96e21e80584f87308ac93c1da (diff)
x86: don't apply __supported_pte_mask to non-present ptes
On an x86 system which doesn't support global mappings, __supported_pte_mask has _PAGE_GLOBAL clear, to make sure it never appears in the PTE. pfn_pte() and so on will enforce it with: static inline pte_t pfn_pte(unsigned long page_nr, pgprot_t pgprot) { return __pte((((phys_addr_t)page_nr << PAGE_SHIFT) | pgprot_val(pgprot)) & __supported_pte_mask); } However, we overload _PAGE_GLOBAL with _PAGE_PROTNONE on non-present ptes to distinguish them from swap entries. However, applying __supported_pte_mask indiscriminately will clear the bit and corrupt the pte. I guess the best fix is to only apply __supported_pte_mask to present ptes. This seems like the right solution to me, as it means we can completely ignore the issue of overlaps between the present pte bits and the non-present pte-as-swap entry use of the bits. __supported_pte_mask contains the set of flags we support on the current hardware. We also use bits in the pte for things like logically present ptes with no permissions, and swap entries for swapped out pages. We should only apply __supported_pte_mask to present ptes, because otherwise we may destroy other information being stored in the ptes. Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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