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

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Jul 11, 2025 at 11:00:06AM +0800, Baolu Lu wrote:
> > > +void iommu_sva_invalidate_kva_range(unsigned long start, unsigned long end)
> > > +{
> > > +	struct iommu_mm_data *iommu_mm;
> > > +
> > > +	if (!static_branch_unlikely(&iommu_sva_present))
> > > +		return;
> > > +
> > > +	guard(spinlock_irqsave)(&iommu_mms_lock);
> > > +	list_for_each_entry(iommu_mm, &iommu_sva_mms, mm_list_elm)
> > > +		mmu_notifier_arch_invalidate_secondary_tlbs(iommu_mm->mm, start, end);
> > > +}
> > 
> > This is absolutely the wrong way to use static_branch. You want them in
> > inline functions guarding the function call, not inside the function
> > call.
> 
> I don't think a static branch is desirable here, as we have no idea how
> often the condition will switch in real-world scenarios. I will remove
> it in the next version if there are no objections.

The point of the static branch was to make the 99% normal case where
SVA has never been used have no-cost in the core MM. I think we should
keep that idea

Jason