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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 10, 2022 at 08:37:43PM +0000, Marc Zyngier wrote:
> 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.


Thanks, I'm reverting these changes for now.
Cindy, once you have your patches ready pinging people who encountered
problems with the previous versions is a very good idea.

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