4ed79ccedd
MipsDoTLBMiss() will load a segmap entry or pde, check that it isn't zero, and then chase that pointer to a physical page. If that page has been freed in the interim, it will read garbage and go on to populate the TLB with it. This can happen because pmap_unwire_ptp zeros out the pde and vm_page_free_zero()s the ptp (or, recursively, zeros out the segmap entry and vm_page_free_zero()s the pdp) without interlocking against MipsDoTLBMiss(). The pmap is locked, and pvh_global_lock may or may not be held, but this is not enough. Solve this issue by inserting TLB shootdowns within _pmap_unwire_ptp(); as MipsDoTLBMiss() runs with IRQs deferred, the IPIs involved in TLB shootdown are sufficient to ensure that MipsDoTLBMiss() sees either a zero segmap entry / pde or a non-zero entry and the pointed-to page still not freed. Submitted by: Nathaniel Filardo <nwf20@cl.cam.ac.uk> Reviewed by: kib MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D24491
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