linux-kernel - Re: [PATCH v8 13/14] remoteproc: qcom: pas: Enable Secure PAS support with IOMMU managed by Linux

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Message-ID: <20251124120318.oqq42ndefnxyihfb@hu-mojha-hyd.qualcomm.com>
Date: Mon, 24 Nov 2025 17:33:18 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....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>,
        Manivannan Sadhasivam <mani@...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 v8 13/14] remoteproc: qcom: pas: Enable Secure PAS
 support with IOMMU managed by Linux

On Mon, Nov 24, 2025 at 12:31:47PM +0100, Konrad Dybcio wrote:
> On 11/21/25 12:01 PM, Mukesh Ojha wrote:
> > Most Qualcomm platforms feature Gunyah hypervisor, which typically
> > handles IOMMU configuration. This includes mapping memory regions and
> > device memory resources for remote processors by intercepting
> > qcom_scm_pas_auth_and_reset() calls. These mappings are later removed
> > during teardown. Additionally, SHM bridge setup is required to enable
> > memory protection for both remoteproc metadata and its memory regions.
> > When the aforementioned hypervisor is absent, the operating system must
> > perform these configurations instead.
> > 
> > When Linux runs as the hypervisor (@ EL2) on a SoC, it will have its
> > own device tree overlay file that specifies the firmware stream ID now
> > managed by Linux for a particular remote processor. If the iommus
> > property is specified in the remoteproc device tree node, it indicates
> > that IOMMU configuration must be handled by Linux. In this case, the
> > has_iommu flag is set for the remote processor, which ensures that the
> > resource table, carveouts, and SHM bridge are properly configured before
> > memory is passed to TrustZone for authentication. Otherwise, the
> > has_iommu flag remains unset, which indicates default behavior.
> > 
> > Enables Secure PAS support for remote processors when IOMMU configuration
> > is managed by Linux.
> > 
> > Signed-off-by: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
> > ---
> 
> [...]
> 
> > +	pas->pas_ctx->has_iommu = rproc->has_iommu;
> > +	pas->dtb_pas_ctx->has_iommu = rproc->has_iommu;
> 
> Sorry if we've been there before, but I see that IOMMU-mapping happens
> before ctx initialization.. can we drop this parameter and just use
> device_iommu_mapped(ctx->dev) in qcom_scm_pas_prepare_and_auth_reset()?

You are right and I am not against it, rproc already has variable `has_iommu`
which we use in framework and vendor driver too, but what I thought,
since this thing we have to do even for Iris or other drivers who are
effected, they already have device which are behind IOMMU and if wrong
device is passed in device_iommu_mapped() instead of firmware device which
could have returned true even when Gunyah is present.

If you feel, has_iommu is not correct name, I could rename it to fw_iommu ?

-- 
-Mukesh Ojha