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Differential D35466

pmap: Keep PTI page table pages busy always
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Authored by markj on Jun 13 2022, 2:12 PM.
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kib
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rGc6d092b5107d: pmap: Keep PTI page table pages busy
Summary

vm_page_free() expects the page to be busied since it belongs to an
object. However, PTI PTPs are never busy, so if a page allocation
failure occurs while mapping user-accessible KVA regions, we panic.

This was effectively an omission from commit
e9ceb9dd110e04fc19729b4e9fb1c8bfbb8398a3. So just keep PTI page table
pages busy.

Reported by: syzkaller

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rG FreeBSD src repository
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Event Timeline

markj created this revision.Jun 13 2022, 2:12 PM
Herald added a subscriber: imp. · View Herald TranscriptJun 13 2022, 2:12 PM
markj requested review of this revision.Jun 13 2022, 2:12 PM
Harbormaster completed remote builds in B45952: Diff 106858.Jun 13 2022, 2:12 PM
kib accepted this revision.Jun 13 2022, 4:08 PM
This revision is now accepted and ready to land.Jun 13 2022, 4:08 PM
markj added a comment.Jun 13 2022, 4:33 PM

Hmm, actually this change might need to go a bit further: pmap_pti_free_page() should use vm_page_xbusy_claim(), at least in principle.

markj updated this revision to Diff 106900.Jun 14 2022, 2:06 PM
  • Claim xbusy before freeing PTI page table pages.
  • Remove some redundant assertions about ref_count, vm_page_unwire_noq() provides the same assertion.
This revision now requires review to proceed.Jun 14 2022, 2:06 PM
Harbormaster completed remote builds in B45967: Diff 106900.Jun 14 2022, 2:06 PM
kib accepted this revision.Jun 14 2022, 5:34 PM
This revision is now accepted and ready to land.Jun 14 2022, 5:34 PM
Closed by commit rGc6d092b5107d: pmap: Keep PTI page table pages busy (authored by markj). · Explain WhyJun 15 2022, 3:39 PM
This revision was automatically updated to reflect the committed changes.
markj added a commit: rGc6d092b5107d: pmap: Keep PTI page table pages busy.

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sys/
amd64/
amd64/
8 lines

Diff 106950

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sys/amd64/amd64/pmap.c

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