Re: [PATCH] virtio-pci: fix up config interrupt handling

[Marc Zyngier]

Hi Michael,

On Sun, 09 Jan 2022 17:49:19 +0000,
"Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> Fixes a couple of issues with irqfd use by config interrupt:
> - Rearrange initialization so cleanup happens in the reverse order
> - Don't use irqfd for config when not in use for data path
> I am not sure this is a complete fix though: I think we
> are better off limiting the effect to vdpa devices
> with config interrupt support. Or even bypass irqfd
> for config completely and inject into KVM using ioctl?
> The advantage would be less FDs used.
> This would mean mostly reverting the patchset though.
> 
> Fixes: d5d24d859c ("virtio-pci: add support for configure interrupt")
> Cc: "Cindy Lu" <lulu@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

This doesn't seem to fix the problems I'm seeing here with a KVM/arm64
guest (the issue exists with and without this patch)

On initial boot:

<quote>
Loading Linux 5.7.0-1-arm64 ...
Loading initial ramdisk ...
qemu-system-aarch64: virtio-blk failed to set guest notifier (-16), ensure 
-accel kvm is set.
qemu-system-aarch64: virtio_bus_start_ioeventfd: failed. Fallback to userspace 
(slower).
qemu-system-aarch64: virtio-scsi: Failed to set guest notifiers (-16), ensure 
-accel kvm is set.
qemu-system-aarch64: virtio_bus_start_ioeventfd: failed. Fallback to userspace 
(slower).
</quote>

The guest is functional though. However, on reboot:

<quote>
Loading Linux 5.7.0-1-arm64 ...
Loading initial ramdisk ...
qemu-system-aarch64: ../hw/pci/msix.c:622: msix_unset_vector_notifiers: 
Assertion `dev->msix_vector_use_notifier && dev->msix_vector_release_notifier' 
failed.
</quote>

Reverting d5d24d859c fixes the issue. For the record, my qemu command
line:

/home/maz/qemu/build/qemu-system-aarch64 -m 1G -smp 8 -cpu host,aarch64=on 
-machine virt,accel=kvm,gic-version=host -nographic -drive 
if=pflash,format=raw,readonly=on,file=/usr/share/AAVMF/AAVMF_CODE.fd -drive 
if=pflash,format=raw,file=bullseye/bBwcgtDY2UwXklV6.fd -netdev user,id=hostnet0 
-device virtio-net-pci,netdev=hostnet0 -drive 
if=none,format=raw,cache=none,aio=native,file=bullseye/bBwcgtDY2UwXklV6.img,id=disk0
 -device virtio-blk-pci,drive=disk0 -drive 
file=debian-testing-arm64-netinst-preseed.iso,id=cdrom,if=none,media=cdrom 
-device virtio-scsi-pci -device scsi-cd,drive=cdrom

Thanks,

        M.

-- 
Without deviation from the norm, progress is not possible.