linux-kernel - Re: Early kernel panic in dmi_decode when running 32-bit kernel on Hyper-V on Windows 11

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Message-ID: <71af4abb-cffd-449e-b397-bd3134d98fb3@gmx.de>
Date: Tue, 16 Apr 2024 23:24:21 +0200
From: Michael Schierl <schierlm@....de>
To: Michael Kelley <mhklinux@...look.com>, Jean Delvare <jdelvare@...e.com>,
 "K. Y. Srinivasan" <kys@...rosoft.com>,
 Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
 Dexuan Cui <decui@...rosoft.com>
Cc: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Early kernel panic in dmi_decode when running 32-bit kernel on
 Hyper-V on Windows 11

Hello,

Am 16.04.2024 um 01:31 schrieb Michael Kelley:

> Can you give me details of the Hyper-V VM configuration?  Maybe
> a screenshot of the Hyper-V Manager "Settings" for the VM would
> be a good starting point, though some of the details are on
> sub-panels in the UI.

It used to be possible to export Hyper-V VM settings as XML, but
apparently that option has been removed in Win2016/Win10, in favor of
their own proprietary binary .vmcx format...

Also, maybe it matters what else Hyper-V is doing. I've installed both
WSL and WSA, and Windows Defender is using Core Isolation Memory
Integrity. I have also enabled support for nested virtualisation in the
Host/Network Switch, but not in that VM.

Anyway, I just created two new VMs (one of each generation) with no hard
disk and everything else default, added a DVD drive to the SCSI
controller of Gen2 (which Gen1 already had on its IDE controller),
disabled Secure Boot on Gen2 and added a second vCPU to Gen1 (which Gen2
already had).

Afterwards, Gen2's dmidecode looks like the summary you posted, and Gen1
reproduces the issue.

> I'm guessing your 32-bit Linux VM is
> a Generation 1 VM.   FWIW, my example was a Generation 2 VM.

Very interesting that Gen2 boots 32-bit Linux better than Gen1 (there is
a delay during hardware autoconfigruation (systemd-udevd) for about 30
seconds when booting Gen2 which I did not investigate yet), despite the
documentation claiming not to use Gen2 for any 32-bit Host OSes.

So I assume this only applies to crappy OSes that directly couple their
bitness to the bitness of the UEFI firmware.

To be fair, the live media I'm using uses Grub's "non-compliant" Linux
loader that bypasses the kernel's EFI stub. When trying with Grub's
"linuxefi" loader, Linux does not boot either, as expected. (On the Gen1
VM, the panic happens regardless whether I use grub's linux16 or linux
loader, and also with SYSLINUX/ISOLINUX loader).

> When you ran a 64-bit Linux and did not have the problem, was
> that with exactly the same Hyper-V VM configuration, or a different
> config?

All my tests were performed with a single (Gen1) VM, and the only
setting I changed was the number of vCPUs.

Regards,

Michael