On Mon, Apr 09, 2018 at 03:57:09PM +0100, Mark Rutland wrote: > On Tue, Feb 06, 2018 at 01:39:15PM +0100, Christoffer Dall wrote: > > On Mon, Nov 27, 2017 at 04:38:03PM +0000, Mark Rutland wrote: > > > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c > > > index 525c01f48867..2205f0be3ced 100644 > > > --- a/arch/arm64/kvm/hyp/switch.c > > > +++ b/arch/arm64/kvm/hyp/switch.c > > > @@ -71,6 +71,8 @@ static void __hyp_text __activate_traps(struct kvm_vcpu > > > *vcpu) > > > { > > > u64 val; > > > > > > + vcpu->arch.host_hcr_el2 = read_sysreg(hcr_el2); > > > + > > > > Looking back at this, it seems excessive to switch this at every > > round-trip. I think it should be possible to have this as a single > > global (or per-CPU) variable that gets restored directly when returning > > from the VM. > > I suspect this needs to be per-cpu, to account for heterogeneous > systems. > > I guess if we move hcr_el2 into kvm_cpu_context, that gives us a > per-vcpu copy for guests, and a per-cpu copy for the host (in the global > kvm_host_cpu_state). > > I'll have a look at how gnarly that turns out. I'm not sure how we can > initialise that sanely for the !VHE case to match whatever el2_setup > did.
There's no harm in jumping down to EL2 to read a register during the initialization phase. All it requires is an annotation of the callee function, and a kvm_call_hyp(), and it's actually quite fast unless you start saving/restoring a bunch of additional system registers. See how we call __kvm_set_tpidr_el2() for example. Thanks, -Christoffer _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm