Hi Community,

We have observed that the 'ht' feature bit cannot be disabled when QEMU runs with KVM acceleration.

qemu-system-x86_64 \
  --enable-kvm \
  -machine q35 \
  -cpu host,-ht \
  -smp 4 \
  -m 4G \
  -drive file=rootfs.img,format=raw \
  -nographic \
  -append 'console=ttyS0 root=/dev/sda rw'

Because '-ht' is specified, the guest should expose no HT capability (cpuid.1.edx[28] = 0), and /proc/cpuinfo shouldn't show HT feature, but we still saw ht in linux guest when run 'cat /proc/cpuinfo'.

XiaoYao mentioned that:

It has been the behavior of QEMU since

  commit 400281af34e5ee6aa9f5496b53d8f82c6fef9319
  Author: Andre Przywara <andre.przyw...@amd.com>
  Date:   Wed Aug 19 15:42:42 2009 +0200

    set CPUID bits to present cores and threads topology

that we cannot remove HT CPUID bit from guest via "-cpu xxx,-ht" if the
VM has >= 2 vcpus.

I'd like to know whether there's a plan to address this issue, or if the current behaviour is considered acceptable.

Best regards,
Ewan.



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