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

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

On 7/16/25 19:57, David Laight wrote:
> On Thu, 10 Jul 2025 17:53:19 +0200
> Peter Zijlstra<peterz@infradead.org> 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...
> Aren't they also somewhat expensive - so you really want to use them
> for configuration options which pretty much don't change.

Yeah! Fair enough.

Thanks,
baolu