Re: [PATCH 02/11] driver core: Set DMA ownership during driver bind/unbind

Jason Gunthorpe
2021-11-15T13:26:02Z

On Mon, Nov 15, 2021 at 05:19:02AM -0800, Christoph Hellwig wrote:
> On Mon, Nov 15, 2021 at 10:05:43AM +0800, Lu Baolu wrote:
> > @@ -566,6 +567,12 @@ static int really_probe(struct device *dev, struct device_driver *drv)
> > goto done;
> > }
> >
> > + if (!drv->suppress_auto_claim_dma_owner) {
> > + ret = iommu_device_set_dma_owner(dev, DMA_OWNER_KERNEL, NULL);
> > + if (ret)
> > + return ret;
> > + }
>
> I'd expect this to go into iommu_setup_dma_ops (and its arm and s390
> equivalents), as that is what claims an IOMMU for in-kernel usage

If iommu_device_set_dma_owner(dev_a) fails changes dynamically
depending on what iommu_device_set_dma_owner(dev_b, DMA_OWNER_USER)
have been done.

The whole point here is that doing a
iommu_device_set_dma_owner(dev_b, DMA_OWNER_USER)
needs to revoke kernel usage from a whole bunch of other devices in
the same group.

revoking kernel usage means it needs to ensure that no driver is bound
and prevent future drivers from being bound.

iommu_setup_dma_ops() is something done once early on in boot, not at
every driver probe, so I don't see how it can help??

Jason