D437 - The direct-memory map never hands a guest physical address zero

Status: decided Date: 2026-09-01

The direct-memory map's default reserves a floor above physical address zero before handing out the first byte of the range.

Why: A conformance probe run against real hardware shows the platform reserves the start of its direct range and never answers a first allocation at zero; a guest that treats a returned zero base as a sentinel needs this to hold.

Rejected: a floor invented to be "large enough" - the measured platform floor is the only value with a source.