Scheduler fixes for hyperthreading

Colin Percival cperciva at freebsd.org
Sat May 21 17:49:29 PDT 2005


Marcel Moolenaar wrote:
> On May 21, 2005, at 4:11 PM, Colin Percival wrote:
>>   The following must be done before hyperthreading is re-enabled:
>> [snip]
> 
> Maybe it's a better idea to describe the problem in much more
> detail, rather than dictate what you want someone else to do?
> A pointer to where the problem is described/discussed would
> do.

The problem is described in my paper "Cache missing for fun and profit":
http://www.daemonology.net/papers/htt.pdf

Put simply, threads which share a processor core can monitor each others'
memory access patterns, so we need to ensure that such co-scheduling never
happens between threads which have different privileges.

The reason I cut through to explaining what needed to be done is that
I discussed this at length with several people from the FreeBSD security
team before and during BSDCan; but these discussions were obviously not
public, so I can't give a reference to them.

Colin Percival


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