OpenBSD/amd64 kernel virtual address space is now 512GB

OpenBSD/amd64 kernel virtual address space is now 512GB

Contributed by<br>Peter N. M. Hansteen<br>on 2026-06-22<br>from the where-would-sir-like-his-640kB? dept.

We almost missed this in a flurry of commits by Jonathan gray (jsg@), but following this commit, OpenBSD/amd64 kernels now have a 512GB address space.

The commit message innocently reads,

List: openbsd-cvs<br>Subject: CVS: cvs.openbsd.org: src<br>From: Jonathan Gray<br>Date: 2026-06-22 0:27:33<br>Message-ID: 162f075352ec66cd () cvs ! openbsd ! org

CVSROOT: /cvs<br>Module name: src<br>Changes by: jsg@cvs.openbsd.org 2026/06/21 18:27:33

Modified files:<br>sys/arch/amd64/include: vmparam.h

Log message:<br>raise the size of amd64 kernel virtual address space from 4G to 512G

This allows mapping all of VRAM on recent Radeon cards where the<br>PCI BAR size is the full (> 4G) size.

Reported by Petre Rodan, who has a Radeon RX 6800 with 16G of VRAM.

feedback from claudio@ ok kettenis@

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