linux-kernel - [REGRESSION] from 74a0e79df68a8042fb84fd7207e57b70722cf825: VFIO PCI passthrough no longer works

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Message-ID: <52914da7-a97b-45ad-86a0-affdf8266c61@mailbox.org>
Date: Tue, 10 Dec 2024 10:04:59 +0100
From: Simon Pilkington <simonp.git@...lbox.org>
To: seanjc@...gle.com
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 regressions@...ts.linux.dev
Subject: [REGRESSION] from 74a0e79df68a8042fb84fd7207e57b70722cf825: VFIO PCI
 passthrough no longer works

Hi,

With the aforementioned commit I am no longer able to use PCI
passthrough to a
Windows guest on the X570 chipset with a 5950X CPU.

The minimal reproducer for me is to attach a GPU to the VM and attempt
to start
Windows setup from an iso image. The VM will apparently livelock at the
setup splash
screen before the spinner appears as one of my CPU cores goes up to 100%
usage
until I force off the VM. This could be very machine-specific though.

Reverting to the old XOR check fixes both 6.12.y stable and 6.13-rc2 for me.
Otherwise they're both bad. Can you please look into it? I can share the
config
I used for test builds if it would help.

Regards,
Simon