Re: [PATCH 4/5] iommu/vt-d: Add support for static identity domain

[Baolu Lu]

On 2023/11/30 4:28, Jason Gunthorpe wrote:
> On Wed, Nov 29, 2023 at 04:26:15PM -0400, Jason Gunthorpe wrote:
> > On Mon, Nov 20, 2023 at 07:29:43PM +0800, Lu Baolu wrote:
> >
> > > @@ -2311,6 +2316,13 @@ static int device_def_domain_type(struct device *dev)
> > >   			return IOMMU_DOMAIN_IDENTITY;
> > >   	}
> > >   
> > > +	/*
> > > +	 * Hardware does not support the passthrough translation mode.
> > > +	 * Always use a dynamaic mapping domain.
> > > +	 */
> > > +	if (!ecap_pass_through(iommu->ecap))
> > > +		return IOMMU_DOMAIN_DMA;
> > > +
> > Doesn't this return from def_domain_type completely prevent using an
> > identity domain?
> >
> > I thought the point of this was to allow the identity domain but have
> > it be translating?
> I suppose the answer is the next patch deletes that stuff.
>
> I would probably have structured this in the other order, first add
> this hunk and say that old HW is being de-supported. Remove all the
> now-dead code creating the 1:1 page table, then refactor the remainder
> to create the global static.

Okay, that would be more readable.

Best regards,
baolu