On 2020-01-13 16:31, Andrew Murray wrote:
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.mur...@arm.com> wrote:
>
> From: Sudeep Holla <sudeep.ho...@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.ho...@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.

> Signed-off-by: Andrew Murray <andrew.mur...@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.

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?

For nVHE, the only reason we'd want to change E2PB on entry/exit of guest
would be if the host is also using SPE. If the host is using SPE whilst
the vcpu is 'loaded' but we're not in the guest, then host SPE could raise
an interrupt - we need the E2PB bits to allow access from EL1 (host).

My comment was of course for VHE. nVHE hardly makes use of load/put at all,
for obvious reasons.

        M.
--
Jazz is not dead. It just smells funny...
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