linux-kernel - Re: [PATCH v4 06/12] firmware: qcom_scm: Add a prep version of auth_and

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Message-ID: <juirzpdb7ltx32fdiu37q3fd543fctvtssnro5qv4satninz2z@3bxup227lvvy>
Date: Tue, 7 Oct 2025 14:37:40 -0700
From: Manivannan Sadhasivam <mani@...nel.org>
To: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
Cc: Bjorn Andersson <andersson@...nel.org>, 
	Mathieu Poirier <mathieu.poirier@...aro.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 06/12] firmware: qcom_scm: Add a prep version of
 auth_and_reset function

On Tue, Oct 07, 2025 at 10:18:51PM +0530, Mukesh Ojha wrote:
> For memory passed to TrustZone (TZ), it must either be part of a pool
> registered with TZ or explicitly registered via SHMbridge SMC calls.
> When Gunyah hypervisor is present, PAS SMC calls from Linux running at
> EL1 are trapped by Gunyah running @ EL2, which handles SHMbridge
> creation for both metadata and remoteproc carveout memory before
> invoking the calls to TZ.
> 
> On SoCs running with a non-Gunyah-based hypervisor, Linux must take
> responsibility for creating the SHM bridge before invoking PAS SMC
> calls. For the auth_and_reset() call, the remoteproc carveout memory
> must first be registered with TZ via a SHMbridge SMC call and once
> authentication and reset are complete, the SHMbridge memory can be
> deregistered.
> 
> Introduce qcom_scm_pas_prepare_and_auth_reset(), which sets up the SHM
> bridge over the remoteproc carveout memory when Linux operates at EL2.
> This behavior is indicated by a new field added to the PAS context data
> structure. The function then invokes the auth_and_reset SMC call.
> 
> Signed-off-by: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
> ---
>  drivers/firmware/qcom/qcom_scm.c       | 48 ++++++++++++++++++++++++++++++++++
>  include/linux/firmware/qcom/qcom_scm.h |  2 ++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index 7b4ff3cb26ed..ab2543d44097 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -791,6 +791,54 @@ int qcom_scm_pas_auth_and_reset(u32 pas_id)
>  }
>  EXPORT_SYMBOL_GPL(qcom_scm_pas_auth_and_reset);
>  
> +/**
> + * qcom_scm_pas_prepare_and_auth_reset() - Prepare, authenticate, and reset the
> + *					   remote processor
> + *
> + * @ctx:	Context saved during call to qcom_scm_pas_context_init()
> + *
> + * This function performs the necessary steps to prepare a PAS subsystem,
> + * authenticate it using the provided metadata, and initiate a reset sequence.
> + *
> + * It should be used when Linux is in control setting up the IOMMU hardware
> + * for remote subsystem during secure firmware loading processes. The preparation
> + * step sets up a shmbridge over the firmware memory before TrustZone accesses the
> + * firmware memory region for authentication. The authentication step verifies
> + * the integrity and authenticity of the firmware or configuration using secure
> + * metadata. Finally, the reset step ensures the subsystem starts in a clean and
> + * sane state.
> + *
> + * Return: 0 on success, negative errno on failure.
> + */
> +int qcom_scm_pas_prepare_and_auth_reset(struct qcom_scm_pas_context *ctx)
> +{
> +	u64 handle;
> +	int ret;
> +
> +	if (!ctx->has_iommu)
> +		return qcom_scm_pas_auth_and_reset(ctx->pas_id);
> +
> +	/*
> +	 * When Linux running @ EL1, Gunyah hypervisor running @ EL2 traps the
> +	 * auth_and_reset call and create an shmbridge on the remote subsystem
> +	 * memory region and then invokes a call to TrustZone to authenticate.
> +	 * When Linux runs @ EL2 Linux must create the shmbridge itself and then
> +	 * subsequently call TrustZone for authenticate and reset.
> +	 */
> +	ret = qcom_tzmem_shm_bridge_create(ctx->mem_phys, ctx->mem_size, &handle);
> +	if (ret) {
> +		dev_err(__scm->dev, "Failed to create shmbridge ret=%d %u\n",

	"Failed to create shmbridge for PAS ID (%u): %d\n"

> +			ret, ctx->pas_id);
> +		return ret;
> +	}
> +
> +	ret = qcom_scm_pas_auth_and_reset(ctx->pas_id);
> +	qcom_tzmem_shm_bridge_delete(handle);
> +
> +	return ret;

	return 0;

- Mani

-- 
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