[PATCH] powerpc/boot: Fix the initrd being overwritten under qemu

[Oliver O'Halloran]

On Wed, Oct 23, 2019 at 10:21 PM Segher Boessenkool
<segher at kernel.crashing.org> wrote:
>
> On Wed, Oct 23, 2019 at 12:36:35PM +1100, Oliver O'Halloran wrote:
> > When booting under OF the zImage expects the initrd address and size to be
> > passed to it using registers r3 and r4. SLOF (guest firmware used by QEMU)
> > currently doesn't do this so the zImage is not aware of the initrd
> > location.  This can result in initrd corruption either though the zImage
> > extracting the vmlinux over the initrd, or by the vmlinux overwriting the
> > initrd when relocating itself.
> >
> > QEMU does put the linux,initrd-start and linux,initrd-end properties into
> > the devicetree to vmlinux to find the initrd. We can work around the SLOF
> > bug by also looking those properties in the zImage.
>
> This is not a bug.  What boot protocol requires passing the initrd start
> and size in GPR3, GPR4?
>
> The CHRP binding (what SLOF implements) requires passing two zeroes here.
> And ePAPR requires passing the address of a device tree and a zero, plus
> something in GPR6 to allow distinguishing what it does.

This is what is assumed by the zImage.pseries. I have no idea where
that assumption comes from,A B

> As Alexey says, initramfs works just fine, so please use that?  initrd was
> deprecated when this code was written already.

That's not what Alexey said and the distinction between an initrd and
an initramfs is completely arbitrary.

>
>
> Segher