Re: [PATCH v3 5/8] iommu/vt-d: Implement def_domain_type iommu ops entry

[Lu Baolu]

Hi Christoph,

On 4/30/19 4:03 AM, Christoph Hellwig wrote:
> > @@ -3631,35 +3607,30 @@ static int iommu_no_mapping(struct device *dev)
> >   	if (iommu_dummy(dev))
> >   		return 1;
> >   
> > -	if (!iommu_identity_mapping)
> > -		return 0;
> > -
>
> FYI, iommu_no_mapping has been refactored in for-next:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu.git/commit/?h=x86/vt-d&id=48b2c937ea37a3bece0094b46450ed5267525289

Oh, yes! Thanks for letting me know this. Will rebase the code.

> >   	found = identity_mapping(dev);
> >   	if (found) {
> > +		/*
> > +		 * If the device's dma_mask is less than the system's memory
> > +		 * size then this is not a candidate for identity mapping.
> > +		 */
> > +		u64 dma_mask = *dev->dma_mask;
> > +
> > +		if (dev->coherent_dma_mask &&
> > +		    dev->coherent_dma_mask < dma_mask)
> > +			dma_mask = dev->coherent_dma_mask;
> > +
> > +		if (dma_mask < dma_get_required_mask(dev)) {
>
> I know this is mostly existing code moved around, but it really needs
> some fixing.  For one dma_get_required_mask is supposed to return the
> required to not bounce mask for the given device.  E.g. for a device
> behind an iommu it should always just return 32-bit.  If you really
> want to check vs system memory please call dma_direct_get_required_mask
> without the dma_ops indirection.
>
> Second I don't even think we need to check the coherent_dma_mask,
> dma_direct is pretty good at always finding memory even without
> an iommu.
>
> Third this doesn't take take the bus_dma_mask into account.
>
> This probably should just be:
>
> 		if (min(*dev->dma_mask, dev->bus_dma_mask) <
> 		    dma_direct_get_required_mask(dev)) {

Agreed and will add this in the next version.

Best regards,
Lu Baolu