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

[Jan Beulich <jbeulich@xxxxxxxx>]

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@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> @@ -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.

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.

Jan