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Differential D55943

arm64: Handle changing self-referential DMAP pages
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Authored by andrew on Thu, Mar 19, 4:04 PM.
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emaste
imp

Details

Reviewers
manu
alc
kib
markj
Group Reviewers
arm64
Summary

Support changing the property of a DMAP page that holds it's own page
table entry.

Because we need to perform a break-before-make sequence to change the
properties of pages a page that also holds it's own page table entry
will fault in the make part of the sequence.

Handle this by mapping the page with a temporary mapping as we already
do when demoting a superpage.

Sponsored by: Arm Ltd

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rG FreeBSD src repository
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Build Status
Buildable 71524
Build 68407: arc lint + arc unit

Event Timeline

andrew created this revision.Thu, Mar 19, 4:04 PM
Herald added a reviewer: manu. · View Herald TranscriptThu, Mar 19, 4:04 PM
Herald added subscribers: emaste, imp. · View Herald Transcript
andrew requested review of this revision.Thu, Mar 19, 4:04 PM
Harbormaster completed remote builds in B71524: Diff 173913.Thu, Mar 19, 4:04 PM
andrew added a child revision: D55944: arm64: mte: cleanup cache register definitions.Thu, Mar 19, 4:04 PM
andrew added reviewers: alc, kib, markj.Thu, Mar 19, 4:25 PM
kib added inline comments.Thu, Mar 19, 10:54 PM
sys/arm64/arm64/pmap.c
8366

IMO it makes more sense to reserve a page frame and use it there instead of allocating and then freeing KVA, similar to the CMAPs on amd64. You would avoid the weird EINVAL from below.

markj added inline comments.Fri, Mar 20, 5:11 AM
sys/arm64/arm64/pmap.c
8366

I agree. It would be better to avoid error cases when updating the kernel pmap.

andrew added inline comments.Mon, Mar 23, 9:51 AM
sys/arm64/arm64/pmap.c
8366

We already return a failure if demote fails above.

markj added inline comments.Mon, Mar 23, 2:52 PM
sys/arm64/arm64/pmap.c
8366

We can remove the first error path in pmap_demote_l2() by implementing kib's suggestion. The second one won't happen for kernel maps. The third one is quite unlikely to happen for kernel maps given that we use VM_ALLOC_INTERRUPT to allocate the new L3 page. I still think it's better to avoid the failure mode here.

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sys/
arm64/
arm64/
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Diff 173913

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sys/arm64/arm64/pmap.c

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