[PATCH v5 0/3] kern/xen: Add Xen command line parsing

From: arraybolt3@gmail.com
To: grub-devel@gnu.org, xen-devel@lists.xenproject.org
Cc: Aaron Rainbolt <arraybolt3@gmail.com>
Subject: [PATCH v5 0/3] kern/xen: Add Xen command line parsing
Date: Wed, 13 Aug 2025 20:36:42 -0500	[thread overview]
Message-ID: <20250814013645.2488043-1-arraybolt3@gmail.com> (raw)

From: Aaron Rainbolt <arraybolt3@gmail.com>

The purpose of this patch is to allow the Xen hypervisor to pass extra
data to GRUB in the form of a kernel command line, allowing the host to
customize the boot process of the guest. The command line from Xen is
parsed, and any variables within that start with the string
`xen_grub_env_` are exposed as environment variables. The grub.cfg
script can then use those environment variables as it sees fit.

The main reason for doing this is to allow implementing boot modes in
Qubes OS while also using in-VM kernels. For more context on Qubes boot
modes, see [1]. In order for this to work with in-VM kernels, it is
necessary for dom0 to pass kernel parameters to the guest without
modifying the guest's grub.cfg manually. This patch allows this to be
done, by allowing dom0 to pass kernel parameters to GRUB, which then
provides them to grub.cfg as an environment variable. The grub.cfg
script within the VM can then append those parameters to the kernel
command line.

All of the changes from version 4 of the patch are simply refinements
after review from Daniel Kiper. The patch's functionality is unchanged.

Since there are substantial changes since version 4, I've re-run the
entire battery of tests that were used against the v4 patch. All tests
pass. As previously, the tests were done by booting a patched GRUB in
Xen with various different parameters passed to it via the Xen-provided
kernel command line. The effects of these parameters on the
bootloader's environment were then tested, and then an Arch Linux image
was booted to ensure that boot still worked.

[1] https://github.com/QubesOS/qubes-linux-pvgrub2/pull/16

Aaron Rainbolt (3):
  include/xen: Rename MAX_GUEST_CMDLINE to GRUB_XEN_MAX_GUEST_CMDLINE
  include/xen: Add warning comment for cmd_line
  kern/xen: Add Xen command line parsing

 docs/grub.texi                |  52 +++++
 grub-core/Makefile.core.def   |   2 +
 grub-core/kern/i386/xen/pvh.c |   4 +
 grub-core/kern/xen/cmdline.c  | 361 ++++++++++++++++++++++++++++++++++
 grub-core/kern/xen/init.c     |   2 +
 include/grub/xen.h            |   2 +
 include/xen/xen.h             |   9 +-
 7 files changed, 430 insertions(+), 2 deletions(-)
 create mode 100644 grub-core/kern/xen/cmdline.c

--
2.50.1

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