On Wed, Feb 09, 2022, Paolo Bonzini wrote: > On 2/9/22 18:07, Sean Christopherson wrote: > > On Wed, Feb 09, 2022, Paolo Bonzini wrote: > > > The TDP MMU has a performance regression compared to the legacy MMU > > > when CR0 changes often. This was reported for the grsecurity kernel, > > > which uses CR0.WP to implement kernel W^X. In that case, each change to > > > CR0.WP unloads the MMU and causes a lot of unnecessary work. When running > > > nested, this can even cause the L1 to hardly make progress, as the L0 > > > hypervisor it is overwhelmed by the amount of MMU work that is needed. > > > > FWIW, my flushing/zapping series fixes this by doing the teardown in an async > > worker. There's even a selftest for this exact case :-) > > > > https://lore.kernel.org/all/20211223222318.1039223-1-seanjc@xxxxxxxxxx > > I'll check it out (it's next on my list as soon as I finally push > kvm/{master,next}, which in turn was blocked by this work). No rush, I need to spin a new version (rebase, and hopefully drop unnecessarily complex be3havior). > But not zapping the roots is even better No argument there :-)
