Re: [PATCH V1] iommu/sva: Fix crash in iommu_sva_unbind_device()

[Lizhi Hou <lizhi.hou@amd.com>]

On 2/28/26 04:14, Yi Liu wrote:
>
> On 2/26/26 06:09, Lizhi Hou wrote:
>>
>>>> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
>>>> index 07d64908a05f..523b8c65c86f 100644
>>>> --- a/drivers/iommu/iommu-sva.c
>>>> +++ b/drivers/iommu/iommu-sva.c
>>>> @@ -179,6 +179,7 @@ void iommu_sva_unbind_device(struct iommu_sva
>>>> *handle)
>>>>               return;
>>>>       }
>>>>
>>>> +     mmgrab(domain->mm);
>>>>       iommu_detach_device_pasid(domain, dev, iommu_mm->pasid);
>>>>       if (--domain->users == 0) {
>>>>               list_del(&domain->next);
>>>> @@ -190,6 +191,7 @@ void iommu_sva_unbind_device(struct iommu_sva
>>>> *handle)
>>>>               if (list_empty(&iommu_sva_mms))
>>>>                       iommu_sva_present = false;
>>>>       }
>>>> +     mmdrop(domain->mm);
>>>>
>>>>       mutex_unlock(&iommu_sva_lock);
>>>>       kfree(handle);
>>>
>>> will moving the below hunk in front of iommu_domain_free() simpler?
>>> Only when (--domain->users == 0), shall the code check if sva_domains
>>> is empty. right?
>>
>> I am not sure if this can be moved in front of iommu_domain_free(). Will
>> iommu_domain_free() be possible to impact sva_domains?
>
> sva_domains is used to track domains associated with the same mm in the
> generic layer. iommu_domain_free() calls vendor iommu driver's free() op
> with domain type specific operations. I don't think it should impact the
> sva_domains.
>
>> iommu_domain_free() calls domain->ops->free(). Could this call back free
>> sva_domain?
>
> I think so. Check intel_mm_free_notifier() as an example.

So if this is true, after calling iommu_domain_free(), the following 
check list_empty(&iommu_mm->sva_domains) could become to true because of 
domain free. If we move the check in front (before iommu_domain_free()), 
the check could be false. That seems leading incorrect iommu_sva_present

Lizhi

>
> Regards,
> Yi Liu
>