On Wed, 2018-01-31 at 13:53 -0800, Jim Mattson wrote: > On Wed, Jan 31, 2018 at 1:42 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > > Can we just say it sucks to be L2 too? :) Because in the end as long as > > no one ever writes to spec_ctrl, everybody is happy. > > Unfortunately, quite a few OS vendors shipped IBRS-based mitigations > earlier this month. (Has Redhat stopped writing to IA32_SPEC_CTRL yet? > :-) > > And in the long run, everyone is going to set IA32_SPEC_CTRL.IBRS=1 on > CPUs with IA32_ARCH_CAPABILITIES.IBRS_ALL. I'm actually working on IBRS_ALL at the moment. I was tempted to *not* let the guests turn it off. Expose SPEC_CTRL but just make it a no-op. Or if that really doesn't fly, perhaps with IBRS_ALL we should invert the logic. Set IBRS to 1 on vCPU reset, and only if it's set to *zero* do we pass through the MSR and set the save_spec_ctrl_on_exit flag. But let's get the code for *current* hardware done first...
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