Re: [PATCH v2 10/18] arm64: KVM/debug: use EL1&0 stage 1 translation regime

Andrew Murray
2019-12-24T11:11:12Z

On Sun, Dec 22, 2019 at 10:34:55AM +0000, Marc Zyngier wrote:
> On Fri, 20 Dec 2019 14:30:17 +0000,
> Andrew Murray <andrew.murray@arm.com> wrote:
> >
> > From: Sudeep Holla <sudeep.holla@arm.com>
> >
> > Now that we have all the save/restore mechanism in place, lets enable
> > the translation regime used by buffer from EL2 stage 1 to EL1 stage 1
> > on VHE systems.
> >
> > Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> > [ Reword commit, don't trap to EL2 ]
>
> Not trapping to EL2 for the case where we don't allow SPE in the
> guest is not acceptable.

Yes understood (because of this I had meant to send the series as RFC btw).

>
> > Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> > ---
> > arch/arm64/kvm/hyp/switch.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> > index 67b7c160f65b..6c153b79829b 100644
> > --- a/arch/arm64/kvm/hyp/switch.c
> > +++ b/arch/arm64/kvm/hyp/switch.c
> > @@ -100,6 +100,7 @@ static void activate_traps_vhe(struct kvm_vcpu *vcpu)
> >
> > write_sysreg(val, cpacr_el1);
> >
> > + write_sysreg(vcpu->arch.mdcr_el2 | 3 << MDCR_EL2_E2PB_SHIFT, mdcr_el2);
> > write_sysreg(kvm_get_hyp_vector(), vbar_el1);
> > }
> > NOKPROBE_SYMBOL(activate_traps_vhe);
> > @@ -117,6 +118,7 @@ static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)
> > __activate_traps_fpsimd32(vcpu);
> > }
> >
> > + write_sysreg(vcpu->arch.mdcr_el2 | 3 << MDCR_EL2_E2PB_SHIFT, mdcr_el2);
>
> There is a _MASK macro that can replace this '3', and is in keeping
> with the rest of the code.

OK.

>
> It still remains that it looks like the wrong place to do this, and
> vcpu_load seems much better. Why should you write to mdcr_el2 on each
> entry to the guest, since you know whether it has SPE enabled at the
> point where it gets scheduled?

Yes OK, I'll move what I can to vcpu_load.

Thanks,

Andrew Murray

>
> M.
>
> --
> Jazz is not dead, it just smells funny.