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authorSvatopluk Kraus <skra@FreeBSD.org>2017-11-02 14:08:38 +0000
committerSvatopluk Kraus <skra@FreeBSD.org>2017-11-02 14:08:38 +0000
commitd18f8e22ec02983a38ca25a4a38dcfb48d1e9aa2 (patch)
tree3d0eed5db4c54419c935f913201bcf8ce0edd494 /secure/usr.bin/openssl/man/pkey.1
parent96ed2690dfb300033e48384704da6ec45737abee (diff)
downloadsrc-d18f8e22ec02983a38ca25a4a38dcfb48d1e9aa2.tar.gz
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Take into account race conditions in case of accessed or modified bit
emulation in fast path of data/prefetch abort common routine. Process these bits only if related page table entries are consistent with provided abort info. In case of inconsistency, do nothing and let processor to signal new abort if still needed. The mapping related to an abort may be a subject of change concurrently. The situation is more evident on multicore machines. Mapping may be removed on one core while being used on another one before TLB flush happened. Memory swapping process may be an example. Or, two or more aborts may be signaled for the same page on more cores concurrently. While an abort on one core may cause a promotion of related mapping, an abort on another core may be inconsistent then as related mapping was promoted. A question is how much real the issue may be on single core machine. However, it's better to play safe even for these machines. This change may solve some "PT2MAP abort" panics reported rarely. The revision of pmap_fault() was initiated thanks to stack backtrace provided by Bob Prohaska (fbsd at www.zefox.net). While here, INVARIANTS block was changed. The previous check had iffy value as only one entry from many was checked from L2 page table. Reviewed by: mmel MFC after: 3 weeks
Notes
Notes: svn path=/head/; revision=325321
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