Messages in this thread | | | Date | Sun, 03 May 2009 19:59:40 +0300 | From | Avi Kivity <> | Subject | Re: [KVM PATCH v3 2/2] kvm: add support for irqfd via eventfd-notification interface |
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Michael S. Tsirkin wrote: > On Mon, Apr 27, 2009 at 02:33:34PM -0400, Gregory Haskins wrote: > >> This allows an eventfd to be registered as an irq source with a guest. Any >> signaling operation on the eventfd (via userspace or kernel) will inject >> the registered GSI at the next available window. >> >> Signed-off-by: Gregory Haskins <ghaskins@novell.com> >> > > If we ever want to use this with e.g. MSI-X emulation in guest, and want > to be stricly compliant to MSI-X, we'll need a way for guest to mask > interrupts, and for host to report that a masked interrupt is pending. > Ideally, all this will be doable with a couple of mmapped pages to avoid > vmexits/system calls. > >
We could do this in two ways:
- move msix entry emulation into the kernel - require the device to support replacing its irqfd, and juggle it like so: - guest disables msi - replace device model fd with eventfd belonging to us - when the device fires its eventfd, set the irq pending bit - guest enables msi - if the pending bit is set, fire the interrupt? - replace device model fd with the real irqfd
I'm leaning towards the latter, though it's not an easy call.
>> +static void >> +irqfd_inject(struct work_struct *work) >> +{ >> + struct _irqfd *irqfd = container_of(work, struct _irqfd, work); >> + struct kvm *kvm = irqfd->kvm; >> + >> + mutex_lock(&kvm->lock); >> + kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1); >> + kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0); >> + mutex_unlock(&kvm->lock); >> > > This will do weird stuff (deliver the irq twice) if the irq is > MSI/MSI-X. I know this was discussed already and is a temporary > shortcut, but maybe add a comment that we really want kvm_toggle_irq, > so that we won't forget? >
If so, that's a bug. MSI should ignore kvm_set_irq(..., 0).
-- error compiling committee.c: too many arguments to function
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