Re: [PATCH v4 5/6] iommu/dma: Simplify calls to iommu_setup_dma_ops()

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Wed, Jun 16, 2021 at 06:02:39PM +0100, Robin Murphy wrote:
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index c62e19bed302..175f8eaeb5b3 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -1322,7 +1322,9 @@ void iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64 dma_limit)
> >   	if (domain->type == IOMMU_DOMAIN_DMA) {
> >   		if (iommu_dma_init_domain(domain, dma_base, dma_limit, dev))
> >   			goto out_err;
> > -		dev->dma_ops = &iommu_dma_ops;
> > +		set_dma_ops(dev, &iommu_dma_ops);
> > +	} else {
> > +		set_dma_ops(dev, NULL);
> 
> I'm not keen on moving this here, since iommu-dma only knows that its own
> ops are right for devices it *is* managing; it can't assume any particular
> ops are appropriate for devices it isn't. The idea here is that
> arch_setup_dma_ops() may have already set the appropriate ops for the
> non-IOMMU case, so if the default domain type is passthrough then we leave
> those in place.
> 
> For example, I do still plan to revisit my conversion of arch/arm someday,
> at which point I'd have to undo this for that reason.

Makes sense, I'll remove this bit.

> Simplifying the base and size arguments is of course fine, but TBH I'd say
> rip the whole bloody lot out of the arch_setup_dma_ops() flow now. It's a
> considerable faff passing them around for nothing but a tenuous sanity check
> in iommu_dma_init_domain(), and now that dev->dma_range_map is a common
> thing we should expect that to give us any relevant limitations if we even
> still care.

So I started working on this but it gets too bulky for a preparatory
patch. Dropping the parameters from arch_setup_dma_ops() seems especially
complicated because arm32 does need the size parameter for IOMMU mappings
and that value falls back to the bus DMA mask or U32_MAX in the absence of
dma-ranges. I could try to dig into this for a separate series.

Even only dropping the parameters from iommu_setup_dma_ops() isn't
completely trivial (8 files changed, 55 insertions(+), 36 deletions(-)
because we still need the lower IOVA limit from dma_range_map), so I'd
rather send it separately and have it sit in -next for a while.

Thanks,
Jean

> 
> That said, those are all things which can be fixed up later if the series is
> otherwise ready to go and there's still a chance of landing it for 5.14. If
> you do have any other reason to respin, then I think the x86 probe_finalize
> functions simply want an unconditional set_dma_ops(dev, NULL) before the
> iommu_setup_dma_ops() call.
> 
> Cheers,
> Robin.
> 
> >   	}
> >   	return;
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 85f18342603c..8d866940692a 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -5165,15 +5165,7 @@ static void intel_iommu_release_device(struct device *dev)
> >   static void intel_iommu_probe_finalize(struct device *dev)
> >   {
> > -	dma_addr_t base = IOVA_START_PFN << VTD_PAGE_SHIFT;
> > -	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> > -	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
> > -
> > -	if (domain && domain->type == IOMMU_DOMAIN_DMA)
> > -		iommu_setup_dma_ops(dev, base,
> > -				    __DOMAIN_MAX_ADDR(dmar_domain->gaw));
> > -	else
> > -		set_dma_ops(dev, NULL);
> > +	iommu_setup_dma_ops(dev, 0, U64_MAX);
> >   }
> >   static void intel_iommu_get_resv_regions(struct device *device,
> > 

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