linux-kernel - Re: [PATCH] drm/msm/a6xx: Skip gpu secure fw load in EL2 mode

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Message-ID: <08440076-3c04-4bb1-b339-071b82d638d2@oss.qualcomm.com>
Date: Mon, 9 Dec 2024 16:03:29 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Rob Clark
 <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Elliot Berman <quic_eberman@...cinc.com>,
        Pavan Kondeti <quic_pkondeti@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] drm/msm/a6xx: Skip gpu secure fw load in EL2 mode

On 9.12.2024 9:19 AM, Akhil P Oommen wrote:
> When kernel is booted in EL2, SECVID registers are accessible to the
> KMD. So we can use that to switch GPU's secure mode to avoid dependency
> on Zap firmware. Also, we can't load a secure firmware without a
> hypervisor that supports it.
> 
> Tested following configurations on sa8775p chipset (Adreno 663 gpu):
> 
> 1. Gunyah (No KVM) - Loads zap shader based on DT
> 2. KVM in VHE - Skips zap shader load and programs SECVID register
> 3. KVM in nVHE - Loads zap shader based on DT
> 4. Kernel in EL2 with CONFIG_KVM=n - Skips zap shader load and
> 	programs SECVID register
> 
> For (1) and (3) configuration, this patch doesn't have any impact.
> Driver loads secure firmware based on other existing hints.
> 
> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
> ---

[...]

> +
> +#ifdef CONFIG_ARM64
> +	/*
> +	 * We can access SECVID_TRUST_CNTL register when kernel is booted in EL2 mode. So, use it
> +	 * to switch the secure mode to avoid the dependency on zap shader.
> +	 */
> +	if (is_kernel_in_hyp_mode())
> +		goto direct_switch;

So I suppose this would ideally be like hv_is_hyperv_initialized()
but for QHEE/Gunyah, which is not going to happen, as we have
millions of devices with old unupstreamable-ABI-Gunyah running..

This looks like the next best things then, so no objections, but..

[...]

> +	ret = a6xx_switch_secure_mode(gpu);
> +	if (!ret)

this should definitely be a if (ret)

Konrad