Differential D19670

Do not preemptively create wired superpage mappings.
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Authored by markj on Mar 21 2019, 4:18 PM.

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Reviewers

kib
alc

Commits

rS345382: Disallow preemptive creation of wired superpage mappings.

Summary

There are some corner cases that can create an unmapped, wired region in
a user address space:

msync(MS_INVALIDATE)
mprotect(PROT_NONE) -> mprotect(PROT_READ)
truncation of a vnode/shm object to a smaller size and back to a larger size

A fault on such a region can trigger preemptive superpage creation
with pmap_enter(PMAP_ENTER_WIRED, psind=1). However, the various
pmaps do not handle this properly and will create a wired superpage
without a leaf page in the pmap's radix tree, so demotion may fail
and cause the address range to be unmapped.

I am not yet sure that we should fix all of the pmaps to handle this,
but for now just make it impossible.

Diff Detail

Repository

rS FreeBSD src repository - subversion

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Event Timeline

markj created this revision.Mar 21 2019, 4:18 PM

Harbormaster completed remote builds in B23232: Diff 55322.Mar 21 2019, 4:18 PM

markj added reviewers: kib, alc.Mar 21 2019, 4:20 PM

kib accepted this revision.Mar 21 2019, 5:16 PM

This revision is now accepted and ready to land.Mar 21 2019, 5:16 PM

Update vm_fault_populate() as well.

This revision now requires review to proceed.Mar 21 2019, 6:49 PM

Harbormaster completed remote builds in B23235: Diff 55327.Mar 21 2019, 6:49 PM

kib accepted this revision.Mar 21 2019, 7:29 PM

This revision is now accepted and ready to land.Mar 21 2019, 7:29 PM

Closed by commit rS345382: Disallow preemptive creation of wired superpage mappings. (authored by markj). · Explain WhyMar 21 2019, 7:53 PM

This revision was automatically updated to reflect the committed changes.

Herald added a subscriber: imp. · View Herald TranscriptMar 21 2019, 7:53 PM

markj mentioned this in rGaa3bcaad5107: amd64: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping.Sep 17 2023, 10:37 AM

markj mentioned this in rGca79521be1b8: amd64: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping.Oct 2 2023, 12:56 PM

markj mentioned this in D41633: riscv pmap: allocate leaf page table page for wired userspace superpages.Nov 6 2023, 4:55 PM

Revision Contents
Changeset List

Path

Size

head/

sys/

amd64/

amd64/

2 lines

i386/

i386/

2 lines

vm/

4 lines

Diff 55329

head/sys/amd64/amd64/pmap.c

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head/sys/i386/i386/pmap.c

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head/sys/vm/vm_fault.c

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