Skip to content

Commit

Permalink
Add docs/pvh.md
Browse files Browse the repository at this point in the history
Brief description of the PVH boot mode.  We defer to Xen for technical
details of how CPU registers are set up upon kernel entry.

Signed-off-by: Colin Percival <[email protected]>
  • Loading branch information
cperciva authored and bchalios committed Aug 14, 2023
1 parent 8a33b00 commit 85c8365
Showing 1 changed file with 15 additions and 0 deletions.
15 changes: 15 additions & 0 deletions docs/pvh.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
# PVH boot mode

Firecracker supports booting x86 kernels in "PVH direct boot" mode
[as specified by the Xen project](https://github.com/xen-project/xen/blob/master/docs/misc/pvh.pandoc).
If a kernel is provided which contains the XEN_ELFNOTE_PHYS32_ENTRY ELF Note
then this boot mode will be used. This boot mode was designed for virtualized
environments which load the kernel directly, and is simpler than the "Linux
boot" mode which is designed to be launched from a legacy boot loader.

PVH boot mode can be enabled for Linux by setting CONFIG_XEN_PVH=y in the
kernel configuration. (This is not the default setting.)

PVH boot mode is enabled by default in FreeBSD, which has support for
Firecracker starting with FreeBSD 14.0. Instructions on building a FreeBSD
kernel and root filesystem are available [here](rootfs-and-kernel-setup.md).

0 comments on commit 85c8365

Please sign in to comment.