Re: [PATCH v6 21/64] KVM: arm64: nv: Handle PSCI call via smc from the guest

Alexandru Elisei
2022-02-04T14:03:41Z

Hi Marc,

The patch looks good to me. Checked kvm_hvc_call_handler(), it returns -1
only when kvm_psci_call() doesn't handle the function and
PSCI_RET_NOT_SUPPORTED must be set by the caller (which is handle_smc).

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>

Thanks,
Alex

On Fri, Jan 28, 2022 at 12:18:29PM +0000, Marc Zyngier wrote:
> From: Jintack Lim <jintack.lim@linaro.org>
>
> VMs used to execute hvc #0 for the psci call if EL3 is not implemented.
> However, when we come to provide the virtual EL2 mode to the VM, the
> host OS inside the VM calls kvm_call_hyp() which is also hvc #0. So,
> it's hard to differentiate between them from the host hypervisor's point
> of view.
>
> So, let the VM execute smc instruction for the psci call. On ARMv8.3,
> even if EL3 is not implemented, a smc instruction executed at non-secure
> EL1 is trapped to EL2 if HCR_EL2.TSC==1, rather than being treated as
> UNDEFINED. So, the host hypervisor can handle this psci call without any
> confusion.
>
> Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/handle_exit.c | 24 ++++++++++++++++++++++--
> 1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 2bbeed8c9786..0cedef6e0d80 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -62,6 +62,8 @@ static int handle_hvc(struct kvm_vcpu *vcpu)
>
> static int handle_smc(struct kvm_vcpu *vcpu)
> {
> + int ret;
> +
> /*
> * "If an SMC instruction executed at Non-secure EL1 is
> * trapped to EL2 because HCR_EL2.TSC is 1, the exception is a
> @@ -69,10 +71,28 @@ static int handle_smc(struct kvm_vcpu *vcpu)
> *
> * We need to advance the PC after the trap, as it would
> * otherwise return to the same address...
> + *
> + * If imm is non-zero, it's not defined, so just skip it.
> + */
> + if (kvm_vcpu_hvc_get_imm(vcpu)) {
> + vcpu_set_reg(vcpu, 0, ~0UL);
> + kvm_incr_pc(vcpu);
> + return 1;
> + }
> +
> + /*
> + * If imm is zero, it's a psci call.
> + * Note that on ARMv8.3, even if EL3 is not implemented, SMC executed
> + * at Non-secure EL1 is trapped to EL2 if HCR_EL2.TSC==1, rather than
> + * being treated as UNDEFINED.
> */
> - vcpu_set_reg(vcpu, 0, ~0UL);
> + ret = kvm_hvc_call_handler(vcpu);
> + if (ret < 0)
> + vcpu_set_reg(vcpu, 0, ~0UL);
> +
> kvm_incr_pc(vcpu);
> - return 1;
> +
> + return ret;
> }
>
> /*
> --
> 2.30.2
>