Re: [PATCH v3 5/7] x86/iommu: remove regions not to be mapped

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Dec 19, 2023 at 05:18:39PM +0100, Jan Beulich wrote:
> On 15.12.2023 15:18, Roger Pau Monne wrote:
> > Introduce the code to remove regions not to be mapped from the rangeset
> > that will be used to setup the IOMMU page tables for the hardware domain.
> > 
> > This change also introduces two new functions: remove_xen_ranges() and
> > vpci_subtract_mmcfg() that copy the logic in xen_in_range() and
> > vpci_is_mmcfg_address() respectively and remove the ranges that would otherwise
> > be intercepted by the original functions.
> > 
> > Note that the rangeset is still not populated.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> 
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> 
> > @@ -533,6 +541,62 @@ void __hwdom_init arch_iommu_hwdom_init(struct domain *d)
> >              goto commit;
> >      }
> >  
> > +    /* Remove any areas in-use by Xen. */
> > +    rc = remove_xen_ranges(map);
> > +    if ( rc )
> > +        panic("IOMMU failed to remove Xen ranges: %d\n", rc);
> > +
> > +    /* Remove any overlap with the Interrupt Address Range. */
> > +    rc = rangeset_remove_range(map, 0xfee00, 0xfeeff);
> > +    if ( rc )
> > +        panic("IOMMU failed to remove Interrupt Address Range: %d\n",
> > +              rc);
> > +
> > +    /* If emulating IO-APIC(s) make sure the base address is unmapped. */
> > +    if ( has_vioapic(d) )
> > +    {
> > +        for ( i = 0; i < d->arch.hvm.nr_vioapics; i++ )
> > +        {
> > +            rc = rangeset_remove_singleton(map,
> > +                PFN_DOWN(domain_vioapic(d, i)->base_address));
> > +            if ( rc )
> > +                panic("IOMMU failed to remove IO-APIC: %d\n",
> > +                      rc);
> > +        }
> > +    }
> > +
> > +    if ( is_pv_domain(d) )
> > +    {
> > +        /*
> > +         * Be consistent with CPU mappings: Dom0 is permitted to establish r/o
> > +         * ones there (also for e.g. HPET in certain cases), so it should also
> > +         * have such established for IOMMUs.  Remove any read-only ranges here,
> > +         * since ranges in mmio_ro_ranges are already explicitly mapped below
> > +         * in read-only mode.
> > +         */
> > +        rc = rangeset_report_ranges(mmio_ro_ranges, 0, ~0UL, map_subtract, map);
> 
> I find it a little odd that you iterate over mmio_ro_ranges twice (once
> here, once in what the earlier patch added), but I guess overall it's
> easier this way.

Given the number of ranges in the MMIO RO rangeset, I'm not sure
there's much reason to attempt to optimize this at the cost of making
the code harder to read.

> Also, nit: Either this line is too long, or ...
> 
> > +        if ( rc )
> > +            panic("IOMMU failed to remove read-only regions: %d\n",
> > +                  rc);
> 
> ... there's no need to wrap lines here.

No need to wrap indeed.

Thanks, Roger.