linux-kernel - Re: [PATCH v19 05/13] of: Add a common kexec FDT setup function

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Date:   Tue, 15 Jun 2021 10:34:48 -0600
From:   Rob Herring <robh@...nel.org>
To:     nramas <nramas@...ux.microsoft.com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will@...nel.org>, Joe Perches <joe@...ches.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        James Morse <james.morse@....com>,
        Sasha Levin <sashal@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Frank Rowand <frowand.list@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Mark Rutland <mark.rutland@....com>, dmitry.kasatkin@...il.com,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Allison Randal <allison@...utok.net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Matthias Brugger <mbrugger@...e.com>,
        Hsin-Yi Wang <hsinyi@...omium.org>, tao.li@...o.com,
        Christophe Leroy <christophe.leroy@....fr>,
        Prakhar Srivastava <prsriva@...ux.microsoft.com>,
        balajib@...ux.microsoft.com,
        linux-integrity <linux-integrity@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v19 05/13] of: Add a common kexec FDT setup function

On Tue, Jun 15, 2021 at 10:13 AM nramas <nramas@...ux.microsoft.com> wrote:
>
> On Tue, 2021-06-15 at 08:01 -0600, Rob Herring wrote:
> > On Tue, Jun 15, 2021 at 6:18 AM Geert Uytterhoeven <
> > geert@...ux-m68k.org> wrote:
> > >
> > > > +void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
> > > > +                                  unsigned long
> > > > initrd_load_addr,
> > > > +                                  unsigned long initrd_len,
> > > > +                                  const char *cmdline, size_t
> > > > extra_fdt_size)
> > > > +{
> > > > +       /* Did we boot using an initrd? */
> > > > +       prop = fdt_getprop(fdt, chosen_node, "linux,initrd-
> > > > start", NULL);
> > > > +       if (prop) {
> > > > +               u64 tmp_start, tmp_end, tmp_size;
> > > > +
> > > > +               tmp_start = fdt64_to_cpu(*((const fdt64_t *)
> > > > prop));
> > > > +
> > > > +               prop = fdt_getprop(fdt, chosen_node,
> > > > "linux,initrd-end", NULL);
> > > > +               if (!prop) {
> > > > +                       ret = -EINVAL;
> > > > +                       goto out;
> > > > +               }
> > > > +
> > > > +               tmp_end = fdt64_to_cpu(*((const fdt64_t *)
> > > > prop));
> > >
> > > Some kernel code assumes "linux,initrd-{start,end}" are 64-bit,
> > > other code assumes 32-bit.
> >
> > It can be either. The above code was a merge of arm64 and powerpc
> > both
> > of which use 64-bit and still only runs on those arches. It looks
> > like
> > some powerpc platforms may use 32-bit, but this would have been
> > broken
> > before.
> of_kexec_alloc_and_setup_fdt() is called from elf_64.c (in
> arch/powerpc/kexec) which is for 64-bit powerpc platform only.

64-bit PPC could be writing 32-bit property values. The architecture
size doesn't necessarily matter. And if the values came from the
bootloader, who knows what size it used.

This code is 32-bit powerpc only?:

arch/powerpc/boot/main.c-       /* Tell the kernel initrd address via
device tree */
arch/powerpc/boot/main.c:       setprop_val(chosen,
"linux,initrd-start", (u32)(initrd_addr));
arch/powerpc/boot/main.c-       setprop_val(chosen,
"linux,initrd-end", (u32)(initrd_addr+initrd_size));

Rob