linux-kernel - Re: x86_64 32-bit EFI mixed mode boot broken

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Message-ID: <CAMj1kXGDnYoz-rF+8JZoMfhGmGqL0PEdvSK8xWH8F4ELXiJB_Q@mail.gmail.com>
Date: Tue, 2 Apr 2024 09:25:10 +0300
From: Ard Biesheuvel <ardb@...nel.org>
To: Clayton Craft <clayton@...ftyguy.net>
Cc: Hans de Goede <hdegoede@...hat.com>, x86@...nel.org, linux-kernel@...r.kernel.org, 
	linux-efi@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, regressions@...ts.linux.dev
Subject: Re: x86_64 32-bit EFI mixed mode boot broken

On Tue, 2 Apr 2024 at 01:44, Clayton Craft <clayton@...ftyguy.net> wrote:
>
> On Sun, 24 Mar 2024 22:53:47 +0200 Ard Biesheuvel <ardb@...nel.org> wrote:
> > > > Thanks.
> > > >
> > > > I pushed another branch
> > > >
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=efi-clayton-3
> > > >
> > > > which has a proper fix for the issue that you found.
> > > >
> > > > As it turns out, the compat mixed mode (with handover protocol) was
> > > >
> > > > broken from the beginning, and the change you identified just happened
> > > >
> > > > to trigger it on your hardware.
> > >
> > >
> > > Tested and fixes booting on my Bay Trail tablet and NUC. Thanks for fixing this!
> > >
> > > Tested-by: Clayton Craft <clayton@...ftyguy.net>
>
> So... maybe my testing wasn't as thorough as I thought, OR I am experiencing an
> unrelated problem. In any case, I'm having some difficulty figuring out what to
> blame. When using this patch on the 6.6 LTS:
>
> 1) kernel seems to panic right after displaying `disabling bootcon [efifb0]`. I
> determined that it's panicking by setting `panic=-1` and seeing it reboot after
> showing that message. I can work around it by setting `keep_bootcon`, but that's
> not ideal.
>

First of all, if you make it all the way to this point, it is unlikely
that this is the same issue. The issue that was fixed was preventing
the boot from proceeding past the very early 32-bit boot stage in the
decompressor, and by the time you hit this panic, the kernel is up an
running.


> 2) kernel complains about no root (from initrd). I can work around this by
> passing `initrd=my-initramfs` on the kernel cmdline.
>

So why is systemd-boot not passing this directly? AFAIK this is the
default method for systemd-boot, and I don't think it implements any
other methods.

> I haven't tried any newer kernels yet. The second issue above makes me wonder if
> your patch related to args might be to blame, but I'm not sure. Any help poking
> around further would be greatly appreciated :)
>

You might try this stable -rc

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/log/?h=linux-6.6.y

which should get released any day now. It has a couple of EFI related
fixes, although none of them seem related in particular.

Another thing you might try is to pass efi=noruntime to the boot, to
check whether EFI is implicated in this to begin with.