Unbinding virtio_pci_modern does not release BAR4 in Linux 6.5.0-rc4

From: Stefan Hajnoczi <stefanha@redhat.com>
To: virtualization@lists.linux-foundation.org
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
	"Michael S. Tsirkin" <mst@redhat.com>
Subject: Unbinding virtio_pci_modern does not release BAR4 in Linux 6.5.0-rc4
Date: Thu, 3 Aug 2023 10:37:18 -0400	[thread overview]
Message-ID: <20230803143718.GA2330143@fedora> (raw)

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Hi,
After running "driverctl --nosave set-override 0000:01:00.0 vfio-pci" on
a virtio-blk-pci device, /proc/iomem shows that BAR4 is still owned by
virtio_pci_modern even though the vfio-pci driver is now bound to the
PCI device.

This regression was introduced after 6.4.7 but I don't see the culprit
in the git logs.

Unfortunately I don't have time to investigate further right now but
I've included instructions on how to reproduce this below.

Can anyone else reproduce this and can we still fix it for the upcoming
Linux 6.5?

Thanks,
Stefan
---
$ qemu-system-x86_64 \
    -M q35,accel=kvm,kernel-irqchip=split \
    -cpu host \
    -m 1G \
    -device intel-iommu,intremap=on,device-iotlb=on \
    --blockdev file,filename=test.img,cache.direct=on,node-name=drive0 \
    --device virtio-blk-pci,drive=drive0 \
    -blockdev file,filename=test2.img,cache.direct=on,node-name=drive2 \
    --device ioh3420,id=pcie.1,chassis=1 \
    --device virtio-blk-pci,disable-legacy=on,disable-modern=off,drive=drive2,iommu_platform=on,ats=on,bus=pcie.1

(guest)# driverctl --nosave set-override 0000:01:00.0 vfio-pci
(guest)# cat /proc/iomem

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