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

[Peter Zijlstra <peterz@infradead.org>]

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?