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path: root/include/asm-i386/pgtable-2level.h
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2006-04-27[PATCH] x86/PAE: Fix pte_clear for the >4GB RAM caseZachary Amsden
Proposed fix for ptep_get_and_clear_full PAE bug. Pte_clear had the same bug, so use the same fix for both. Turns out pmd_clear had it as well, but pgds are not affected. The problem is rather intricate. Page table entries in PAE mode are 64-bits wide, but the only atomic 8-byte write operation available in 32-bit mode is cmpxchg8b, which is expensive (at least on P4), and thus avoided. But it can happen that the processor may prefetch entries into the TLB in the middle of an operation which clears a page table entry. So one must always clear the P-bit in the low word of the page table entry first when clearing it. Since the sequence *ptep = __pte(0) leaves the order of the write dependent on the compiler, it must be coded explicitly as a clear of the low word followed by a clear of the high word. Further, there must be a write memory barrier here to enforce proper ordering by the compiler (and, in the future, by the processor as well). On > 4GB memory machines, the implementation of pte_clear for PAE was clearly deficient, as it could leave virtual mappings of physical memory above 4GB aliased to memory below 4GB in the TLB. The implementation of ptep_get_and_clear_full has a similar bug, although not nearly as likely to occur, since the mappings being cleared are in the process of being destroyed, and should never be dereferenced again. But, as luck would have it, it is possible to trigger bugs even without ever dereferencing these bogus TLB mappings, even if the clear is followed fairly soon after with a TLB flush or invalidation. The problem is that memory above 4GB may now be aliased into the first 4GB of memory, and in fact, may hit a region of memory with non-memory semantics. These regions include AGP and PCI space. As such, these memory regions are not cached by the processor. This introduces the bug. The processor can speculate memory operations, including memory writes, as long as they are committed with the proper ordering. Speculating a memory write to a linear address that has a bogus TLB mapping is possible. Normally, the speculation is harmless. But for cached memory, it does leave the falsely speculated cacheline unmodified, but in a dirty state. This cache line will be eventually written back. If this cacheline happens to intersect a region of memory that is not protected by the cache coherency protocol, it can corrupt data in I/O memory, which is generally a very bad thing to do, and can cause total system failure or just plain undefined behavior. These bugs are extremely unlikely, but the severity is of such magnitude, and the fix so simple that I think fixing them immediately is justified. Also, they are nearly impossible to debug. Signed-off-by: Zachary Amsden <zach@vmware.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-23[PATCH] i386: actively synchronize vmalloc area when registering certain ↵Jan Beulich
callbacks Registering a callback handler through register_die_notifier() is obviously primarily intended for use by modules. However, the way these currently get called it is basically impossible for them to actually be used by modules, as there is, on non-PAE configurationes, a good chance (the larger the module, the better) for the system to crash as a result. This is because the callback gets invoked (a) in the page fault path before the top level page table propagation gets carried out (hence a fault to propagate the top level page table entry/entries mapping to module's code/data would nest infinitly) and (b) in the NMI path, where nested faults must absolutely not happen, since otherwise the IRET from the nested fault re-enables NMIs, potentially resulting in nested NMI occurences. Besides the modular aspect, similar problems would even arise for in- kernel consumers of the API if they touched ioremap()ed or vmalloc()ed memory inside their handlers. Signed-off-by: Jan Beulich <jbeulich@novell.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-30[PATCH] i386: little pgtable.h consolidation vs 2/3levelPaolo 'Blaisorblade' Giarrusso
Join together some common functions (pmd_page{,_kernel}) over 2level and 3level pages. Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Acked-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-04-16Linux-2.6.12-rc2Linus Torvalds
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!