> From: Jan Beulich <jbeul...@suse.com>
> Sent: Monday, April 11, 2022 5:37 PM
>
> The field taking the value 7 (resulting in 18-bit DIDs when using the
> calculation in cap_ndoms(), when the DID fields are only 16 bits wide)
> is reserved. Instead of misbehaving in case we would encounter such an
> IOMMU, refuse to use it.
>
> Signed-off-by: Jan Beulich <jbeul...@suse.com>
Reviewed-by: Kevin Tian <kevin.t...@intel.com>
>
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -1267,8 +1267,11 @@ int __init iommu_alloc(struct acpi_drhd_
>
> quirk_iommu_caps(iommu);
>
> + nr_dom = cap_ndoms(iommu->cap);
> +
> if ( cap_fault_reg_offset(iommu->cap) +
> cap_num_fault_regs(iommu->cap) * PRIMARY_FAULT_REG_LEN >
> PAGE_SIZE ||
> + ((nr_dom - 1) >> 16) /* I.e. cap.nd > 6 */ ||
> (has_register_based_invalidation(iommu) &&
> ecap_iotlb_offset(iommu->ecap) >= PAGE_SIZE) )
> {
> @@ -1294,8 +1297,6 @@ int __init iommu_alloc(struct acpi_drhd_
> if ( !ecap_coherent(iommu->ecap) )
> iommu_non_coherent = true;
>
> - nr_dom = cap_ndoms(iommu->cap);
> -
> if ( nr_dom <= DOMID_MASK * 2 + cap_caching_mode(iommu->cap) )
> {
> /* Allocate domain id (bit) maps. */
