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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Thu, 20 Apr 2023 09:54:40 +0200
Message-ID: <CAMj1kXF1eaORsUPk=8Mam8OCQbfcMEBca=Lr2tdN=nihiDqb=Q@mail.gmail.com>
Subject: Re: [RFC PATCH 0/3] efi: Implement generic zboot support
To:     Gerd Hoffmann <kraxel@redhat.com>
Cc:     linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        Evgeniy Baskov <baskov@ispras.ru>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexey Khoroshilov <khoroshilov@ispras.ru>,
        Peter Jones <pjones@redhat.com>,
        Dave Young <dyoung@redhat.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        Kees Cook <keescook@chromium.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
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On Thu, 20 Apr 2023 at 08:07, Gerd Hoffmann <kraxel@redhat.com> wrote:
>
>   Hi,
>
> > > Realistically, the second option is unlikely to ever be used on x86,
> > >
> > > What would be needed to do so?  Teach kexec-tools and grub2 parse and
> > > load zboot kernels I guess?
> >
> > I already implemented this for mach-virt here, so we can load Fedora
> > kernels without firmware:
> >
> > https://gitlab.com/qemu-project/qemu/-/commit/ff11422804cd03494cc98691eecd3909ea09ab6f
> >
> > On arm64, this is probably more straight-forward, as the bare metal
> > image is already intended to be booted directly like that. However,
> > the x86 uncompressed image requires surprisingly little from all the
> > boot_params/setup_header cruft to actually boot, so perhaps there it
> > is easy too.
>
> For existing boot loaders like grub I'd expect it being easy
> to code up, all the setup header code exists already, grub also
> has support for uncompressing stuff, so it should really be only
> zboot header parsing and some plumbing to get things going (i.e.
> have grub boot efi zboot kernels in bios mode).
>
> Disclaimer: didn't actually check grub source code.
>

I have :-(

> I suspect the bigger problem wrt. grub is that getting patches merged
> upstream is extremely slow and every distro carries a huge stack of
> patches ...
>

Yeah, Daniel has been asking me about LoadFile2 initrd loading support
for x86, so I think getting things merged is not going to be a problem
(although it will still take some time) - I can just implement it and
send it out at the same time.

But hacking/building/running GRUB is a rather painful experience, so I
have been kicking this can down the road.