646c9e0d6a
Doing so ensures that all threads sharing the pmap have a consistent view of the mapping. This fixes the problem described in the commit log message for r329254 without the overhead of an extra page fault in the common case. (Now that all pmap_enter() implementations are similarly modified, the workaround added in r329254 can be removed, reducing the overhead of COW faults.) With this change we can reuse the PV entry from the old mapping, potentially avoiding a call to reclaim_pv_chunk(). Otherwise, there is nothing preventing the old PV entry from being reclaimed. In rare cases this could result in the PTE's page table page being freed, leading to a use-after-free of the page when the updated PTE is written following the allocation of the PV entry for the new mapping. Reviewed by: br, markj MFC after: 3 weeks Differential Revision: https://reviews.freebsd.org/D16261 |
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