Re: [PATCH v3 28/28] docs: update Xen-on-KVM documentation

[Andrew Cooper]

On 25/10/2023 7:26 pm, David Woodhouse wrote:

> On Wed, 2023-10-25 at 13:20 -0500, Eric Blake wrote:
> > On Wed, Oct 25, 2023 at 03:50:42PM +0100, David Woodhouse wrote:
> >       
> > > +
> > > +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
> > >         
> > Is the space between -- and console= intentionsl?
> >       
> Yes, that one is correct. The -- is how you separate Xen's command line
> (on the left) from the guest kernel command line (on the right).
>     
    
    To expand on this a bit.
    
    Multiboot1 supports multiple modules but only a single command
    line.  As one of the modules passed to Xen is the dom0 kernel, we
    need some way to pass it's command line, hence the " -- ".
    
    Multiboot2 and PVH support a command line per module, which is the
    preferred way to pass the commandlines, given a choice.
    
    ~Andrew