Re: [PATCH v2 1/1] iommu/sva: Invalidate KVA range on kernel TLB flush

[Baolu Lu <baolu.lu@linux.intel.com>]

On 7/10/25 23:53, Peter Zijlstra wrote:
> On Thu, Jul 10, 2025 at 03:54:32PM +0200, Peter Zijlstra wrote:
> 
>>> @@ -132,8 +136,15 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
>>>   	if (ret)
>>>   		goto out_free_domain;
>>>   	domain->users = 1;
>>> -	list_add(&domain->next, &mm->iommu_mm->sva_domains);
>>>   
>>> +	if (list_empty(&iommu_mm->sva_domains)) {
>>> +		scoped_guard(spinlock_irqsave, &iommu_mms_lock) {
>>> +			if (list_empty(&iommu_sva_mms))
>>> +				static_branch_enable(&iommu_sva_present);
>>> +			list_add(&iommu_mm->mm_list_elm, &iommu_sva_mms);
>>> +		}
>>> +	}
>>> +	list_add(&domain->next, &iommu_mm->sva_domains);
>>>   out:
>>>   	refcount_set(&handle->users, 1);
>>>   	mutex_unlock(&iommu_sva_lock);
>>> @@ -175,6 +186,15 @@ void iommu_sva_unbind_device(struct iommu_sva *handle)
>>>   		list_del(&domain->next);
>>>   		iommu_domain_free(domain);
>>>   	}
>>> +
>>> +	if (list_empty(&iommu_mm->sva_domains)) {
>>> +		scoped_guard(spinlock_irqsave, &iommu_mms_lock) {
>>> +			list_del(&iommu_mm->mm_list_elm);
>>> +			if (list_empty(&iommu_sva_mms))
>>> +				static_branch_disable(&iommu_sva_present);
>>> +		}
>>> +	}
>>> +
>>>   	mutex_unlock(&iommu_sva_lock);
>>>   	kfree(handle);
>>>   }
>>
>> This seems an odd coding style choice; why the extra unneeded
>> indentation? That is, what's wrong with:
>>
>> 	if (list_empty()) {
>> 		guard(spinlock_irqsave)(&iommu_mms_lock);
>> 		list_del();
>> 		if (list_empty()
>> 			static_branch_disable();
>> 	}
> 
> Well, for one, you can't do static_branch_{en,dis}able() from atomic
> context...
> 
> Was this ever tested?

I conducted unit tests for vmalloc()/vfree() scenarios, and Yi performed
fuzzing tests. We have not observed any warning messages. Perhaps
static_branch_disable() is not triggered in the test cases?

Thanks,
baolu