On Thu, 2023-10-26 at 10:25 +0100, David Woodhouse wrote: > > > So it would have been entirely possible to use -initrd 'bzImage > > console=hvc0 root=/dev/xvda1' if Xen worked like that. > > Xen does allow that too. I didn't realise our multiboot loader did though. > > So yes, you *can* use -initrd 'bzImage root=/dev/xvda1'. > > And you can even load more than one module, it seems. Separate them by > commas, so -initrd 'bzImage,initrd.img' should work. > > You can even do both at the same time. If you have commas on the kernel > command line, *double* them: > > -initrd 'bzImage root=/dev/xvda earlyprintk=xen,,keep,initrd.img' > > I'll update the documentation accordingly. https://git.infradead.org/users/dwmw2/qemu.git/commitdiff/0b13c0ae39b +Booting Xen PV guests +--------------------- + +Booting PV guest kernels is possible by using the Xen PV shim (a version of Xen +itself, designed to run inside a Xen HVM guest and provide memory management +services for one guest alone). + +The Xen binary is provided as the ``-kernel`` and the guest kernel itself (or +PV Grub image) as the ``-initrd`` image, which actually just means the first +multiboot "module". For example: + +.. parsed-literal:: + + |qemu_system| --accel kvm,xen-version=0x40011,kernel-irqchip=split \\ + -chardev stdio,id=char0 -device xen-console,chardev=char0 \\ + -display none -m 1G -kernel xen -initrd bzImage \\ + -append "pv-shim console=xen,pv -- console=hvc0 root=/dev/xvda1" \\ + -drive file=${GUEST_IMAGE},if=xen + +The Xen image must be built with the ``CONFIG_XEN_GUEST`` and ``CONFIG_PV_SHIM`` +options, and as of Xen 4.17, Xen's PV shim mode does not support using a serial +port; it must have a Xen console or it will panic. + +The example above provides the guest kernel command line after a separator +(" ``--`` ") on the Xen command line, and does not provide the guest kernel +with an actual initramfs, which would need to listed as a second multiboot +module. For more complicated alternatives, see the +:ref:`documentation <initrd-reference-label>` for the ``-initrd`` option. + I also fixed up the -initrd documentation so that it actually mentions how to quote commas, using a Xen PV launch as an example: ``-initrd "file1 arg=foo,file2"`` This syntax is only available with multiboot. - Use file1 and file2 as modules and pass arg=foo as parameter to the - first module. + Use file1 and file2 as modules and pass ``arg=foo`` as parameter to the + first module. Commas can be provided in module parameters by doubling + them on the command line to escape them: + +``-initrd "bzImage earlyprintk=xen,,keep root=/dev/xvda1,initrd.img"`` + Multiboot only. Use bzImage as the first module with + "``earlyprintk=xen,keep root=/dev/xvda1``" as its command line, + and initrd.img as the second module.
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