Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
From:   Daniel Drake <drake@endlessm.com>
Date:   Fri, 16 Aug 2019 14:14:12 +0800
Message-ID: <CAD8Lp47V5G+3UfEzt9wNRr7U-RdLAdCO7JFLQ+QF1JbkuhCcPg@mail.gmail.com>
Subject: Early EFI-related boot freeze in parse_setup_data()
To:     linux-efi@vger.kernel.org,
        Linux Kernel <linux-kernel@vger.kernel.org>, x86@kernel.org
Cc:     Linux Upstreaming Team <linux@endlessm.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi,

We're working with a new consumer MiniPC based on AMD E1-7010.

It fails to boot Linux when booting in EFI mode - it hangs with
nothing on screen. earlycon=efifb doesn't show any output.

Looking closer, I was able to confirm that we reach EFI
ExitBootServices() via efi_printk in the efi stub. But you can't use
EFI's console functionality after that point, so I then resorted to
inserting calls to:

   idt_invalidate(NULL); __asm__ __volatile__("int3");

throughout the early boot code that follows in order to force a system
reset. That way I could deduce if execution was reaching that point
(system reset) or not (system hang as before). As a side-question I'd
be curious if there is any better way to debug such early boot
failures on consumer x86 hardware without a serial port...

Anyway, the system freeze occurs in parse_setup_data(), specifically:

        data = early_memremap(pa_data, sizeof(*data));
        data_len = data->len + sizeof(struct setup_data);

Dereferencing data->len causes the system to hang. I presume it
triggers an exception handler due to some kind of invalid memory
access.

By returning early in that function, boot continues basically fine. So
I could then log the details: pa_data has value 0x892bb018 and
early_memremap returns address 0xffffffffff200018. Accessing just a
single byte at that address causes the system hang.

This original pa_data value (from boot_params.hdr.setup_data) was set
by the EFI stub in setup_efi_pci(). I confirmed that the same
0x892bb018 value is set there, it is not being corrupted along the
way.

Any suggestions for how to diagnose further?

dmesg output:
https://gist.github.com/dsd/199bed7b590e90efdf73f9f6384ca551

Thanks
Daniel