Re: Hyper-Threading Vulnerability

Andi Kleen
2005-05-15T09:37:06Z

> I was under the impression that P4 and later processors do not vary the
> TSC rate when doing frequency scaling. This is mentioned in the
> documentation for the high res timers patch.

Prescott and later do not vary TSC, but P4s before that do.
On x86-64 it is true because only Nocona is supported which has a
pstate invariant TSC.

The latest x86-64 kernel has a special X86_CONSTANT_TSC internal
CPUID bit, which is set in that case. If some other subsystem
uses it I would recommend to port that to i386 too.

-Andi