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

[Tushar Dave <tdave@nvidia.com>]

On 4/25/25 05:00, Jason Gunthorpe wrote:
> 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

Yup. And I should be adding similar check (i.e. max_pasid > 0 ) before invoking 
set_dev_pasid and remove_dev_pasid (as Kevin already asked earlier).
I can do that in v2.

-Tushar

> 
> Jason