[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v8 15/17] x86/ctxt: Issue a speculation barrier between vcpu contexts
On Mon, 2018-01-15 at 14:23 +0100, David Woodhouse wrote: > > > > > > > Also... if you're doing that in context_switch() does it do the right > > > thing with idle? If a CPU switches to the idle domain and then back > > > again to the same vCPU, does that do the IBPB twice? > > > > Context switches to idle will skip the IBPB because it isn't needed, but > > any switch to non-idle need it. In your example, we should execute just > > a single IBPB. > > In my example I think we should not execute IBPB at all. We come from a > given VMCS, sleep for a while, and go back to it. No need for any > flushing whatsoever. msw points out that in my example we *don't* execute IBPB at all, I think. In both switching to idle, and back to the vCPU, we should hit this case and not the 'else' case that does the IBPB: 1710 if ( (per_cpu(curr_vcpu, cpu) == next) || 1711 (is_idle_domain(nextd) && cpu_online(cpu)) ) 1712 { 1713 local_irq_enable(); 1714 } Attachment:
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