There's an upstream build failure on ARM (not directly related to Xen but rather some other config options it enables). The xen package is x86_64-only anyways.
···521521 ${optionalString (versionAtLeast version "3.13") ''
522522 KVM_VFIO y
523523 ''}
524524- XEN? y
525525- XEN_DOM0? y
526526- ${optionalString ((versionAtLeast version "3.18") && (features.xen_dom0 or false)) ''
527527- PCI_XEN? y
528528- HVC_XEN? y
529529- HVC_XEN_FRONTEND? y
530530- XEN_SYS_HYPERVISOR? y
531531- SWIOTLB_XEN? y
532532- XEN_BACKEND? y
533533- XEN_BALLOON? y
534534- XEN_BALLOON_MEMORY_HOTPLUG? y
535535- XEN_EFI? y
536536- XEN_HAVE_PVMMU? y
537537- XEN_MCE_LOG? y
538538- XEN_PVH? y
539539- XEN_PVHVM? y
540540- XEN_SAVE_RESTORE? y
541541- XEN_SCRUB_PAGES? y
542542- XEN_SELFBALLOONING? y
543543- XEN_STUB? y
544544- XEN_TMEM? y
524524+ ${optionalString (stdenv.isx86_64 || stdenv.isi686) ''
525525+ XEN? y
526526+ XEN_DOM0? y
527527+ ${optionalString ((versionAtLeast version "3.18") && (features.xen_dom0 or false)) ''
528528+ PCI_XEN? y
529529+ HVC_XEN? y
530530+ HVC_XEN_FRONTEND? y
531531+ XEN_SYS_HYPERVISOR? y
532532+ SWIOTLB_XEN? y
533533+ XEN_BACKEND? y
534534+ XEN_BALLOON? y
535535+ XEN_BALLOON_MEMORY_HOTPLUG? y
536536+ XEN_EFI? y
537537+ XEN_HAVE_PVMMU? y
538538+ XEN_MCE_LOG? y
539539+ XEN_PVH? y
540540+ XEN_PVHVM? y
541541+ XEN_SAVE_RESTORE? y
542542+ XEN_SCRUB_PAGES? y
543543+ XEN_SELFBALLOONING? y
544544+ XEN_STUB? y
545545+ XEN_TMEM? y
546546+ ''}
545547 ''}
546548 KSM y
547549 ${optionalString (!stdenv.is64bit) ''