On 07/12/20 18:41, Thomas Gleixner wrote:
Right this happens still occasionally, but for quite some time this is
100% firmware sillyness and not a fundamental property of the hardware
anymore.
It's still a fundamental property of old hardware. Last time I tried to
kill support for processors earlier than Core 2, I had to revert it.
That's older than Nehalem.
We try to catch such situation in KVM instead of blowing up but
this may still result in subtle bugs I believe. Maybe we would be better
off killing all VMs in case TSC ever gets unsynced (by default).
I just ran a guest on an old machine with unsynchronized TSCs and was
able to observe clock monotonic going backwards between two threads
pinned on two vCPUs, which _is_ bad. Getting unsynced clocks reliably
under control is extremly hard.
Using kvmclock? (Half serious: perhaps a good reason to have per-vCPU
offsets is to be able to test what happens with unsynchronized TSCs...).
Paolo
