Re: [PATCH v10 03/24] iommu: generalize the batched sync after map interface

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Apr 29, 2025 at 10:19:46AM +0800, Baolu Lu wrote:
> > -int iommu_map(struct iommu_domain *domain, unsigned long iova,
> > -	      phys_addr_t paddr, size_t size, int prot, gfp_t gfp)
> > +int iommu_sync_map(struct iommu_domain *domain, unsigned long iova, size_t size)
> >   {
> >   	const struct iommu_domain_ops *ops = domain->ops;
> > -	int ret;
> > -
> > -	might_sleep_if(gfpflags_allow_blocking(gfp));
> > -	/* Discourage passing strange GFP flags */
> > -	if (WARN_ON_ONCE(gfp & (__GFP_COMP | __GFP_DMA | __GFP_DMA32 |
> > -				__GFP_HIGHMEM)))
> > -		return -EINVAL;
> > +	if (!ops->iotlb_sync_map)
> > +		return 0;
> > +	return ops->iotlb_sync_map(domain, iova, size);
> > +}
> 
> I am wondering whether iommu_sync_map() needs a return value. The
> purpose of this callback is just to sync the TLB cache after new
> mappings are created, which should effectively be a no-fail operation.

Yeah, it is pretty much nonsense, the other flushes don't fail:

	void (*flush_iotlb_all)(struct iommu_domain *domain);
	int (*iotlb_sync_map)(struct iommu_domain *domain, unsigned long iova,
			      size_t size);
	void (*iotlb_sync)(struct iommu_domain *domain,
			   struct iommu_iotlb_gather *iotlb_gather);

> Furthermore, currently no iommu driver implements this callback in a way
> that returns a failure. 

Given s390 does weirdly fail sync_map but not sync this needs a bigger
touch than just that.

But what I really want to do is get rid of iotlb_sync_map and replace it
with iotlb_sync, and feed the gather through the iommu_map path.

It doesn't really make sense to have a special interface for this.

So I think this patch is fine as is..

Jason