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Hot-unplug is usually tracked, implemented and tested as a separate feature, due to the additional complexity.

This bug was initially created as a copy of Bug #1454803

OVMF (built from upstream edk2 @ f78c8bf2c64f ("OvmfPkg/README: document 4MB flash layout", 2017-05-06)), using the SMM stack, does not implement VCPU hotplug / hot-unplug.

Investigate & implement the feature.

It will almost certainly require upstream QEMU development too.

The upstream v9 series:

* [edk2-devel] [PATCH v9 00/10] support CPU hot-unplug
msgid: <20210312062656.2477515-1-ankur.a.arora>
https://edk2.groups.io/g/devel/message/72702
https://listman.redhat.com/archives/edk2-devel-archive/2021-March/msg00449.html

has been merged as commit range 4751a48aeb2a..f3bdfc41866e, via <https://github.com/tianocore/edk2/pull/1494>.

Hi Laszlo, 

Would you please set DTM? The qemu bug 1849172 is ON_QA, QE would like to know when the edk2 package is ready to test. Thanks!

QE bot(pre verify): Set 'Verified:Tested,SanityOnly' as gating/tier1 test pass.

Verify:
qemu-kvm-6.0.0-21.module+el8.5.0+11555+e0ab0d09
kernel-4.18.0-315.el8.x86_64
edk2-ovmf-20210527gite1999b264f1f-1.el8.noarch
Guest: RHEL.8.5.0, Win2022

Ran a round test of cpu hotplug/unplug under ovmf, all cases passed.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Moderate: edk2 security, bug fix, and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2021:4198