[PATCH] vm: optional 16K-page guest kernel builds

[colbyt <colby@colbyt.com>]

From: PolymerOS Coordinator <coordinator@polymeros.local>

KVM hosts with a 16K stage-2 granule (Apple Silicon machines running
upstream kernels, NVIDIA GB10) can only run guests whose kernel is built
with ARM64_16K_PAGES. Add an optional kernelPageSize argument to the app
and net VM kernel builds; the default is unchanged. A 16K-page guest
Image built this way has booted to a full session under a 16K host here
since June without issues on my side.
---
Following up on the offer in my July 7 mail, as a standalone patch now
that the nixpkgs update brings Linux 7.1. The config delta is five
lines; the edit (an argument defaulting to today's behavior) is a
proposal — happy to rework it if you'd rather structure it differently,
e.g. hang it off a single shared helper instead of two arguments.

 spectrum/img/app/default.nix    | 7 +++++++
 spectrum/vm/sys/net/default.nix | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/img/app/default.nix b/img/app/default.nix
index 06dfc86c..6b839f0f 100644
--- a/img/app/default.nix
+++ b/img/app/default.nix
@@ -7,6 +7,7 @@ import ../../lib/call-package.nix (
 , cryptsetup
 , erofs-utils, jq, lndir, s6-rc, util-linux
 , cacert, linux_latest
+, kernelPageSize ? null
 }:
 
 let
@@ -49,6 +50,12 @@ let
       VSOCKETS = yes;
       VIRTIO_VSOCKETS = yes;
       VT = no;
+    } // lib.optionalAttrs (kernelPageSize == "16k") {
+      # KVM hosts with a 16K stage-2 granule (e.g. Apple Silicon, NVIDIA
+      # GB10) can only run guests whose kernel uses 16K pages.
+      ARM64_4K_PAGES = lib.mkForce no;
+      ARM64_16K_PAGES = lib.mkForce yes;
+      ARM64_64K_PAGES = lib.mkForce no;
     };
   }).overrideAttrs ({ installFlags ? [], ... }: {
     installFlags = installFlags ++ [
diff --git a/vm/sys/net/default.nix b/vm/sys/net/default.nix
index 3ec34a7f..efd1c8e1 100644
--- a/vm/sys/net/default.nix
+++ b/vm/sys/net/default.nix
@@ -10,6 +10,7 @@ pkgsMusl.callPackage (
 , erofs-utils, jq, lndir, s6-rc, util-linux
 , busybox, dbus, execline, iwd, kmod, linuxPackagesFor, linux_latest
 , mdevd, nftables, s6, s6-linux-init, spectrum-driver-tools, xdp-tools
+, kernelPageSize ? null
 }:
 
 let
@@ -52,6 +53,12 @@ let
       VIRTIO_CONSOLE = yes;
       VIRTIO_PCI = yes;
       VT = no;
+    } // lib.optionalAttrs (kernelPageSize == "16k") {
+      # KVM hosts with a 16K stage-2 granule (e.g. Apple Silicon, NVIDIA
+      # GB10) can only run guests whose kernel uses 16K pages.
+      ARM64_4K_PAGES = lib.mkForce no;
+      ARM64_16K_PAGES = lib.mkForce yes;
+      ARM64_64K_PAGES = lib.mkForce no;
     };
   }).overrideAttrs ({ installFlags ? [], ... }: {
     installFlags = installFlags ++ [
-- 
2.55.0