linux-kernel - Re: [PATCH v5 17/27] iommu/arm-smmu-v3-kvm: Probe SMMU HW

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Message-ID: <20251128170748.GE812105@ziepe.ca>
Date: Fri, 28 Nov 2025 13:07:48 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Mostafa Saleh <smostafa@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvmarm@...ts.linux.dev, iommu@...ts.linux.dev,
	catalin.marinas@....com, will@...nel.org, maz@...nel.org,
	oliver.upton@...ux.dev, joey.gouly@....com, suzuki.poulose@....com,
	yuzenghui@...wei.com, joro@...tes.org, jean-philippe@...aro.org,
	praan@...gle.com, danielmentz@...gle.com, mark.rutland@....com,
	qperret@...gle.com, tabba@...gle.com
Subject: Re: [PATCH v5 17/27] iommu/arm-smmu-v3-kvm: Probe SMMU HW

On Mon, Nov 17, 2025 at 06:48:04PM +0000, Mostafa Saleh wrote:

> +/*
> + * Mini-probe and validation for the hypervisor.
> + */
> +static int smmu_probe(struct hyp_arm_smmu_v3_device *smmu)
> +{
> +	u32 reg;
> +
> +	/* IDR0 */
> +	reg = readl_relaxed(smmu->base + ARM_SMMU_IDR0);
> +	smmu->features = smmu_idr0_features(reg);
> +
> +	/*
> +	 * Some MMU600 and MMU700 have errata that prevent them from using nesting,
> +	 * not sure how can we identify those, so it's recommended not to enable this
> +	 * drivers on such systems.
> +	 * And preventing any of those will be too restrictive
> +	 */

This driver is doing nesting though ??

Shouldn't you detect those IPs and not support a S1 at all so there is
no nesting? Identity only?

Jason