On a Thursday in 2025, Jiri Denemark via Devel wrote:
From: Jiri Denemark <jdenemar@redhat.com>
The feature does not do anything, QEMU will always set it according to the CPU topology completely ignoring what we asked for. Unfortunately, the way the state of "ht" is reported changed in QEMU 10.0.0 (commit c6bd2dd634208).
QEMU older than 10.0.0 would just report whatever was specified on the command line totally ignoring the actual state of the feature visible to a guest. But after the change QEMU reports ht=on in case it enabled "ht" based on the CPU topology. In all other cases QEMU still reports the state requested on the command line.
As a result of this change a domain with multiple CPU threads started on QEMU < 10.0.0 could not be migrated to QEMU >= 10.0.0 unless "ht" was explicitly enabled in the domain XML because libvirt would see "ht" enabled on the destination, but disabled on the source (the guest would see "ht" enabled in both cases anyway). Outgoing migration of domains started on QEMU >= 10.0.0 is not affected.
To fix this issue we can completely ignore "ht" both in the domain XML and in the CPU properties reported by QEMU. With this fix incoming migration to QEMU >= 10.0.0 works again.
https://issues.redhat.com/browse/RHEL-104216
Signed-off-by: Jiri Denemark <jdenemar@redhat.com> --- src/qemu/qemu_capabilities.c | 1 + tests/qemuxmlconfdata/cpu-cache-disable3.x86_64-latest.args | 2 +- .../cpu-check-default-partial.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-exact2-nofallback.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-exact2-nofallback.x86_64-latest.xml | 1 - tests/qemuxmlconfdata/cpu-exact2-nofallback.xml | 1 - tests/qemuxmlconfdata/cpu-exact2.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-exact2.x86_64-latest.xml | 1 - tests/qemuxmlconfdata/cpu-exact2.xml | 1 - tests/qemuxmlconfdata/cpu-host-model-cmt.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-host-model-vendor.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-minimum1.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-minimum2.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-phys-bits-emulate2.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-strict1.x86_64-latest.args | 2 +- tests/qemuxmlconfdata/cpu-strict1.x86_64-latest.xml | 1 - tests/qemuxmlconfdata/cpu-strict1.xml | 1 - tests/qemuxmlconfdata/cpu-tsc-frequency.x86_64-latest.args | 2 +- 18 files changed, 12 insertions(+), 17 deletions(-)
Reviewed-by: Ján Tomko <jtomko@redhat.com> Jano