linux-kernel - Re: [PATCH v7 28/45] arm64: rme: support RSI_HOST

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Message-ID: <12b5ba41-4b1e-4876-9796-d1d6bb344015@redhat.com>
Date: Tue, 4 Mar 2025 16:01:16 +1000
From: Gavin Shan <gshan@...hat.com>
To: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
 kvmarm@...ts.linux.dev
Cc: Joey Gouly <joey.gouly@....com>, Catalin Marinas
 <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
 Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
 Oliver Upton <oliver.upton@...ux.dev>,
 Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
 <yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Alexandru Elisei <alexandru.elisei@....com>,
 Christoffer Dall <christoffer.dall@....com>, Fuad Tabba <tabba@...gle.com>,
 linux-coco@...ts.linux.dev,
 Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
 Shanker Donthineni <sdonthineni@...dia.com>, Alper Gun
 <alpergun@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>
Subject: Re: [PATCH v7 28/45] arm64: rme: support RSI_HOST_CALL

On 2/14/25 2:14 AM, Steven Price wrote:
> From: Joey Gouly <joey.gouly@....com>
> 
> Forward RSI_HOST_CALLS to KVM's HVC handler.
> 
> Signed-off-by: Joey Gouly <joey.gouly@....com>
> Signed-off-by: Steven Price <steven.price@....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