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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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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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Build Status

Buildable 71530
Build 68413: arc lint + arc unit

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
8310	Please update this comment.
8438	Can the comment please explain why this is necessary?
8450	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
8450	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.

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
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sys/

arm64/

arm64/

55 lines

include/

1 line

Diff 173919

sys/arm64/arm64/pmap.c

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sys/arm64/include/pmap.h

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