Re: [PATCH v7 28/45] arm64: rme: support RSI_HOST_CALL

Gavin Shan
2025-03-04T06:01:28Z

On 2/14/25 2:14 AM, Steven Price wrote:
> From: Joey Gouly <joey.gouly@arm.com>
>
> Forward RSI_HOST_CALLS to KVM's HVC handler.
>
> Signed-off-by: Joey Gouly <joey.gouly@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Changes since v4:
> * Setting GPRS is now done by kvm_rec_enter() rather than
> rec_exit_host_call() (see previous patch - arm64: RME: Handle realm
> enter/exit). This fixes a bug where the registers set by user space
> were being ignored.
> ---
> arch/arm64/kvm/rme-exit.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/arch/arm64/kvm/rme-exit.c b/arch/arm64/kvm/rme-exit.c
> index c785005f821f..4f7602aa3c6c 100644
> --- a/arch/arm64/kvm/rme-exit.c
> +++ b/arch/arm64/kvm/rme-exit.c
> @@ -107,6 +107,26 @@ static int rec_exit_ripas_change(struct kvm_vcpu *vcpu)
> return -EFAULT;
> }
>
> +static int rec_exit_host_call(struct kvm_vcpu *vcpu)
> +{
> + int ret, i;
> + struct realm_rec *rec = &vcpu->arch.rec;
> +
> + vcpu->stat.hvc_exit_stat++;
> +
> + for (i = 0; i < REC_RUN_GPRS; i++)
> + vcpu_set_reg(vcpu, i, rec->run->exit.gprs[i]);
> +
> + ret = kvm_smccc_call_handler(vcpu);
> +
> + if (ret < 0) {
> + vcpu_set_reg(vcpu, 0, ~0UL);
> + ret = 1;
> + }
> +
> + return ret;
> +}
> +

I don't understand how a negative error can be returned from kvm_smccc_call_handler().
Besides, SMCCC_RET_NOT_SUPPORTED has been set to GPR[0 - 3] if the request can't be
supported. Why we need to set GPR[0] to ~0UL, which corresponds to SMCCC_RET_NOT_SUPPORTED
if I'm correct. I guess change log or a comment to explain the questions would be
nice.

> static void update_arch_timer_irq_lines(struct kvm_vcpu *vcpu)
> {
> struct realm_rec *rec = &vcpu->arch.rec;
> @@ -168,6 +188,8 @@ int handle_rec_exit(struct kvm_vcpu *vcpu, int rec_run_ret)
> return rec_exit_psci(vcpu);
> case RMI_EXIT_RIPAS_CHANGE:
> return rec_exit_ripas_change(vcpu);
> + case RMI_EXIT_HOST_CALL:
> + return rec_exit_host_call(vcpu);
> }
>
> kvm_pr_unimpl("Unsupported exit reason: %u\n",

Thanks,
Gavin