OpenBSD/amd64 kernel virtual address space is now 512GB

Contributed by Peter N. M. Hansteen on 2026-06-22 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
Subject:    CVS: cvs.openbsd.org: src
From:       Jonathan Gray <jsg () cvs ! openbsd ! org>
Date:       2026-06-22 0:27:33
Message-ID: 162f075352ec66cd () cvs ! openbsd ! org

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

Modified files:
	sys/arch/amd64/include: vmparam.h 

Log message:
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
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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