amd64/pmap: Return la57 in amd nested page
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Authored by aokblast on Jun 30 2026, 9:14 PM.

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rGef26f64c1122: amd64/pmap: Return la57 in amd nested page

Summary

AMD doesn't encode page depth in eptp. As a result, the page level is
decided by the host la57 value. Without this, it uses 4 level page and
therefore cause machine enable la57 have garbage page translation.

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rG FreeBSD src repository

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Event Timeline

aokblast created this revision.Jun 30 2026, 9:14 PM

Herald added a subscriber: imp. · View Herald TranscriptJun 30 2026, 9:14 PM

aokblast requested review of this revision.Jun 30 2026, 9:14 PM

Harbormaster completed remote builds in B74435: Diff 181118.Jun 30 2026, 9:14 PM

@kib I don't have the machine now so it needs test from the user.

kib accepted this revision.Jun 30 2026, 10:52 PM

This revision is now accepted and ready to land.Jun 30 2026, 10:52 PM

This patch has made bhyve work on modern AMD CPUs for us.

root@mortis:~ # sysctl hw.model
hw.model: AMD EPYC 9845 160-Core Processor

root@mortis:~ # uname -a
FreeBSD mortis.local.abi.am 16.0-CURRENT FreeBSD 16.0-CURRENT #0 arcpatch-D57978-n286987-9ccbd8092c1a: Fri Sep 11 06:53:09 UTC 2026     root@mortis.local.abi.am:/usr/obj/usr/src/amd64.amd64/sys/GENERIC amd64

root@mortis:~ # sysctl vm.pmap.la57
vm.pmap.la57: 1

Before this path being applied, bhyve would just get stuck.

Thank you all!

Closed by commit rGef26f64c1122: amd64/pmap: Return la57 in amd nested page (authored by aokblast, committed by markj). · Explain WhyFri, Sep 11, 1:02 PM

This revision was automatically updated to reflect the committed changes.

markj added a commit: rGef26f64c1122: amd64/pmap: Return la57 in amd nested page.