linux-kernel - Re: [PATCH rc] iommu: Skip PASID validation for devices without PASID capability

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Message-ID: <20250425120035.GA1804142@nvidia.com>
Date: Fri, 25 Apr 2025 09:00:35 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Tushar Dave <tdave@...dia.com>
Cc: Vasant Hegde <vasant.hegde@....com>,
	Baolu Lu <baolu.lu@...ux.intel.com>, joro@...tes.org,
	will@...nel.org, robin.murphy@....com, kevin.tian@...el.com,
	yi.l.liu@...el.com, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH rc] iommu: Skip PASID validation for devices without
 PASID capability

On Thu, Apr 24, 2025 at 05:49:20PM -0700, Tushar Dave wrote:

> In the above topology, we setup ACS flags on DSP 0008:02:03.0 and
> 0008:02:00.0 to achieve desired p2p configuration for GPU and DMA-PF.
> Apparently, this creates multi-device group with GPU being only device with
> PASID support in that group. In this case, set_dev_pasid() ops invoked for
> each device within the group with pasid=1 and doesn't fail.

Hurm, it doesn't fail, but it corrupts memory in the driver :\

int arm_smmu_set_pasid(struct arm_smmu_master *master,
		       struct arm_smmu_domain *smmu_domain, ioasid_t pasid,
		       struct arm_smmu_cd *cd, struct iommu_domain *old)
{
	struct iommu_domain *sid_domain = iommu_get_domain_for_dev(master->dev);
	struct arm_smmu_attach_state state = {
		.master = master,
		.ssid = pasid,
		.old_domain = old,
	};
	struct arm_smmu_cd *cdptr;
	int ret;

	/* The core code validates pasid */
                ^^^^^^^^^^

Which is not true after this patch.

The core code may not call the driver's set_pasid() function with a PASID
larger than that specific device's device->dev->iommu->max_pasids

Jason