linux-kernel - RE: [PATCH v2 2/2] iommu: Probe right iommu

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Date: Mon, 29 Jan 2024 08:07:34 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Jason Gunthorpe <jgg@...pe.ca>,
	"Joerg Roedel" <joro@...tes.org>, Will Deacon <will@...nel.org>, Robin Murphy
	<robin.murphy@....com>
CC: "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 2/2] iommu: Probe right iommu_ops for device

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Friday, January 26, 2024 6:54 PM
> 
> Previously, in the iommu probe device path, __iommu_probe_device() gets
> the iommu_ops for the device from dev->iommu->fwspec if this field has
> been initialized before probing. Otherwise, it is assumed that only one
> of Intel, AMD, s390, PAMU or legacy SMMUv2 can be present, hence it's
> feasible to lookup the global iommu device list and use the iommu_ops of
> the first iommu device which has no dev->iommu->fwspec.
> 
> The assumption mentioned above is no longer correct with the introduction
> of the IOMMUFD mock device on x86 platforms. There might be multiple
> instances of iommu drivers, none of which have the dev->iommu->fwspec
> field populated.
> 
> Probe the right iommu_ops for device by iterating over all the global
> drivers and call their probe function to find a match.
> 
> Fixes: 17de3f5fdd35 ("iommu: Retire bus ops")
> Cc: Robin Murphy <robin.murphy@....com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>

Reviewed-by: Kevin Tian <kevin.tian@...el.com>, with a nit:

> +
> +	mutex_lock(&iommu_device_lock);
> +	list_for_each_entry(iter, &iommu_device_list, list) {
> +		iommu_dev = __iommu_do_probe_device(dev, iter->ops);
> +		if (!IS_ERR(iommu_dev))
> +			break;
> +	}

here could skip iommu with a valid fwspec.