We have just published Qubes Security Bulletin (QSB) #058: Insufficient cache write-back under VT-d (XSA-321). The text of this QSB is reproduced below. This QSB and its accompanying signatures will always be available in the Qubes Security Pack (qubes-secpack).
This is a companion discussion topic for the original entry at https://www.qubes-os.org/news/2020/07/07/qsb-058/