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Differential D41633

riscv pmap: allocate leaf page table page for wired userspace superpages
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Authored by bnovkov on Aug 29 2023, 2:21 PM.
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imp
mhorne
riscv

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markj
kib
alc
Commits
rG998d0babdde6: riscv: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping
rGd0941ed9b5c3: riscv: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping
Summary

This patch fixes a syzkaller issue regarding wired userspace superpages by allocating a leaf page table page for wired userspace superpages.

The original issue is an edge case that creates an unmapped, wired region in userspace. Subsequent faults on this region can trigger wired superpage creation, leading to a panic upon demotion as the pmap does not create a leaf page table page for the wired superpage. D19670 fixed this by disallowing preemptive creation of wired superpage mappings, but that fix is currently interfering with an ongoing effort of speeding up vm_map_wire for large, contiguous entries (e.g. bhyve wiring guest memory) .

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Event Timeline

bnovkov created this revision.Aug 29 2023, 2:21 PM
Herald added subscribers: riscv, imp. · View Herald TranscriptAug 29 2023, 2:21 PM
bnovkov requested review of this revision.Aug 29 2023, 2:21 PM
bnovkov added reviewers: kib, alc.Sep 16 2023, 4:44 PM
markj accepted this revision.Sep 17 2023, 11:22 AM
This revision is now accepted and ready to land.Sep 17 2023, 11:22 AM
mhorne added a subscriber: mhorne.Oct 10 2023, 5:09 PM

Is there a reason this hasn't been merged but the versions for other architectures have?

If it's a matter of testing, please let me know.

markj added a comment.Oct 10 2023, 7:00 PM
In D41633#961575, @mhorne wrote:

Is there a reason this hasn't been merged but the versions for other architectures have?

If it's a matter of testing, please let me know.

There are some pmap changes that I've ported over to riscv that we'd like to rebase this patch on top of. I just need to test my patch for that, hopefully this week.

markj added a comment.Oct 19 2023, 6:38 PM
In D41633#961615, @markj wrote:
In D41633#961575, @mhorne wrote:

Is there a reason this hasn't been merged but the versions for other architectures have?

If it's a matter of testing, please let me know.

There are some pmap changes that I've ported over to riscv that we'd like to rebase this patch on top of. I just need to test my patch for that, hopefully this week.

The above mentioned changes are in a patch series on phabricator now: https://reviews.freebsd.org/D42287

Also here: https://github.com/markjdb/freebsd/commits/riscv-pmap-improvements

markj added a comment.Nov 6 2023, 4:55 PM

Sorry for the delayed reply. The above-mentioned riscv pmap commits are in main now - @bojan.novkovic_fer.hr would it be possible to rebase on top of that? Then I can commit this patch, and we can finally revert D19670.

bnovkov updated this revision to Diff 129832.Nov 7 2023, 6:14 PM

Rebased the patch.

This revision now requires review to proceed.Nov 7 2023, 6:14 PM
bnovkov added a comment.Nov 7 2023, 6:15 PM
In D41633#969403, @markj wrote:

Sorry for the delayed reply. The above-mentioned riscv pmap commits are in main now - @bojan.novkovic_fer.hr would it be possible to rebase on top of that? Then I can commit this patch, and we can finally revert D19670.

No problem, thank you for taking the time to work on those commits.
I've updated the patch on top of your changes.

This revision was not accepted when it landed; it landed in state Needs Review.Nov 8 2023, 12:32 PM
Closed by commit rGd0941ed9b5c3: riscv: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping (authored by bnovkov, committed by markj). · Explain Why
This revision was automatically updated to reflect the committed changes.
markj added a commit: rGd0941ed9b5c3: riscv: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping.
markj added a comment.Nov 8 2023, 12:39 PM
In D41633#969735, @bojan.novkovic_fer.hr wrote:
In D41633#969403, @markj wrote:

Sorry for the delayed reply. The above-mentioned riscv pmap commits are in main now - @bojan.novkovic_fer.hr would it be possible to rebase on top of that? Then I can commit this patch, and we can finally revert D19670.

No problem, thank you for taking the time to work on those commits.
I've updated the patch on top of your changes.

Would you like to do the honours of reverting the vm_fault change? :)

bnovkov added a comment.Nov 8 2023, 8:18 PM
In D41633#969928, @markj wrote:

Would you like to do the honours of reverting the vm_fault change? :)

Of course! I've created a revision.

markj added a commit: rG998d0babdde6: riscv: Add a leaf PTP when pmap_enter(psind=1) creates a wired mapping.Dec 2 2023, 9:56 PM

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sys/riscv/riscv/pmap.c

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