Re: [PATCH v5 10/11] powerpc/pseries/iommu: Make use of DDW for indirect mapping

[Frederic Barrat]

On 21/07/2021 05:32, Alexey Kardashevskiy wrote:
> > > +        struct iommu_table *newtbl;
> > > +        int i;
> > > +
> > > +        for (i = 0; i < ARRAY_SIZE(pci->phb->mem_resources); i++) {
> > > +            const unsigned long mask = IORESOURCE_MEM_64 | 
> > > IORESOURCE_MEM;
> > > +
> > > +            /* Look for MMIO32 */
> > > +            if ((pci->phb->mem_resources[i].flags & mask) == 
> > > IORESOURCE_MEM)
> > > +                break;
> > > +        }
> > > +
> > > +        if (i == ARRAY_SIZE(pci->phb->mem_resources))
> > > +            goto out_del_list;
> >
> >
> > So we exit and do nothing if there's no MMIO32 bar?
> > Isn't the intent just to figure out the MMIO32 area to reserve it when 
> > init'ing the table? In which case we could default to 0,0
> >
> > I'm actually not clear why we are reserving this area on pseries.
>
>
>
> If we do not reserve it, then the iommu code will allocate DMA pages 
> from there and these addresses are MMIO32 from the kernel pov at least. 
> I saw crashes when (I think) a device tried DMAing to the top 2GB of the 
> bus space which happened to be a some other device's BAR.


hmmm... then figuring out the correct range needs more work. We could 
have more than one MMIO32 bar. And they don't have to be adjacent. I 
don't see that we are reserving any range on the initial table though 
(on pseries).

  Fred