On Thu, 2019-06-27 at 14:11 +0200, Thomas Gleixner wrote: > On Thu, 27 Jun 2019, Xiaoyao Li wrote: > > On 6/27/2019 3:12 PM, Thomas Gleixner wrote: > > > The real interesting question is whether the #AC on split lock prevents > > > the > > > actual bus lock or not. If it does then the above is fine. > > > > > > If not, then it would be trivial for a malicious guest to set the > > > SPLIT_LOCK_ENABLE bit and "handle" the exception pro forma, return to the > > > offending instruction and trigger another one. It lowers the rate, but > > > that > > > doesn't make it any better. > > > > > > The SDM is as usual too vague to be useful. Please clarify. > > > > > > > This feature is to ensure no bus lock (due to split lock) in hardware, that > > to > > say, when bit 29 of TEST_CTL is set, there is no bus lock due to split lock > > can be acquired. > > So enabling this prevents the bus lock, i.e. the exception is raised before > that happens. > exactly. > Please add that information to the changelog as well because that's > important to know and makes me much more comfortable handing the #AC back > into the guest when it has it enabled. > Will add it in next version. Thanks.
