[BUG]smt sysfs dir missing on 4.4.148 and 4.14.63

Hi Greg, hi Thomas,

I noticed /sys/devices/system/cpu/smt dir is missing on 4.4.148 and 4.14.63, default setting.

Tried stable/master branch 31130a16d459 ("Merge tag 'for-linus-4.19-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip") It's the same there.

When boot with 'nosmt' kernel paramter kernel 4.14.63 panic during boot, 4.4.148 boot fine. The call trace seem irq related, is it known bug?

Thanks