On Sun, May 05, 2019 at 04:56:42PM +0800, Peter Xu wrote: > When assigning kvm irqfd we didn't check the irqchip mode but we allow > KVM_IRQFD to succeed with all the irqchip modes. However it does not > make much sense to create irqfd even without the kernel chips. Let's > provide a arch-dependent helper to check whether a specific irqfd is > allowed by the arch. At least for x86, it should make sense to check: > > - when irqchip mode is NONE, all irqfds should be disallowed, and, > > - when irqchip mode is SPLIT, irqfds that are with resamplefd should > be disallowed. > > For either of the case, previously we'll silently ignore the irq or > the irq ack event if the irqchip mode is incorrect. However that can > cause misterious guest behaviors and it can be hard to triage. Let's > fail KVM_IRQFD even earlier to detect these incorrect configurations. > > CC: Paolo Bonzini <pbonzini@xxxxxxxxxx> > CC: Radim Krčmář <rkrcmar@xxxxxxxxxx> > CC: Alex Williamson <alex.williamson@xxxxxxxxxx> > CC: Eduardo Habkost <ehabkost@xxxxxxxxxx> > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> Note: haven't tested, but IIUC QEMU's vfio will naturally fall back to no-irqfd mode (actually virtio seems to also have this but virtio should not be affected after all) if the KVM_IRQFD ioctl failed so I feel like this patch could also at least fix the broken guests reported besides any future fixes from QEMU side on the issue: https://bugs.launchpad.net/qemu/+bug/1826422 Thanks, -- Peter Xu
