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Differential D55949

arm64: Support changing the DMAP memory type
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Authored by andrew on Mar 19 2026, 4:05 PM.
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manu
alc
kib
markj
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arm64
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rGa780d21eab97: arm64: Support changing the DMAP memory type
Summary

When MTE is enabled we will use the DMAP to manage tags. To be able to
read/write them we need to change the memory attribute to
VM_MEMATTR_TAGGED.

Support changing the DMAP memory type to values known to have
equivalent cache properties.

Sponsored by: Arm Ltd

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rG FreeBSD src repository
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Event Timeline

andrew created this revision.Mar 19 2026, 4:05 PM
Herald added a reviewer: manu. · View Herald TranscriptMar 19 2026, 4:05 PM
Herald added subscribers: emaste, imp. · View Herald Transcript
andrew requested review of this revision.Mar 19 2026, 4:05 PM
Harbormaster completed remote builds in B71530: Diff 173919.Mar 19 2026, 4:05 PM
andrew added a parent revision: D55948: arm64: mte: add tagged memory attribute.Mar 19 2026, 4:05 PM
andrew added a child revision: D55950: arm64: Support some per-thread sctlr_el1 fields.
andrew added reviewers: alc, kib, markj.Mar 19 2026, 4:25 PM
markj added inline comments.Mar 23 2026, 2:10 AM
sys/arm64/arm64/pmap.c
8382–8386

Please update this comment.

8520

Can the comment please explain why this is necessary?

8533

Suppose we update a range with mode == VM_MEMATTR_WRITE_BACK, and dmap_attr != VM_MEMATTR_WRITE_BACK. Then, a subsequent update of the same range with old_mode == VM_MEMATTR_WRITE_BACK will not update the DMAP entries, which seems like a bug.

andrew added inline comments.Apr 13 2026, 2:13 PM
sys/arm64/arm64/pmap.c
8533

The only way we can currently get here with old_mode != -1 is through pmap_change_dmap_attr so will have old_mode == dmap_attr so the memory will be updated.

If we find other uses for old_mode then we may need to be smarter about handling old_mode for DMAP regions.

andrew updated this revision to Diff 175435.Apr 13 2026, 2:26 PM

Update comments

Harbormaster completed remote builds in B72176: Diff 175435.Apr 13 2026, 2:26 PM
This revision was not accepted when it landed; it landed in state Needs Review.May 27 2026, 3:24 PM
Closed by commit rGa780d21eab97: arm64: Support changing the DMAP memory type (authored by andrew). · Explain Why
This revision was automatically updated to reflect the committed changes.
andrew added a commit: rGa780d21eab97: arm64: Support changing the DMAP memory type.

Revision Contents
Changeset List

PathSize
sys/
arm64/
arm64/
64 lines
include/
1 line

Diff 178735

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sys/arm64/arm64/pmap.c

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sys/arm64/include/pmap.h

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