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: <20251127072324.ogy3hlv5k26veqbq@hu-mojha-hyd.qualcomm.com>
Date: Thu, 27 Nov 2025 12:53:24 +0530
From: Mukesh Ojha <mukesh.ojha@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        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 Wed, Nov 26, 2025 at 10:40:51AM -0600, Bjorn Andersson wrote:
> On Mon, Nov 24, 2025 at 05:33:18PM +0530, Mukesh Ojha wrote:
> > 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 ?
> > 
> 
> While this does relate to "has_iommu" and/or "fw_iommu" when it comes to
> the current PAS context, the "feature flag" is "should we use tzmem or
> not".
> 
> Further, in the case of the modem, we don't have an IOMMU, but we still
> need to set this flag on the ctx in order to get the metadata into TZ.
> 
> So, I think this should be detached from the "iommu". How about naming
> the "has_iommu" in the context to "use_tzmem"?

Sure, this way it gets attached to tzmem alloc/create API to be used or
not for PIL SMC calls.

> 
> Regards,
> Bjorn
> 
> > -- 
> > -Mukesh Ojha

-- 
-Mukesh Ojha