linux-kernel - Re: [PATCH 2/4] kvm: Add missing KVM

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Date:	Sun, 24 Jun 2012 08:56:17 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	avi@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	jan.kiszka@...mens.com
Subject: Re: [PATCH 2/4] kvm: Add missing KVM_IRQFD API documentation

On Sun, 2012-06-24 at 11:34 +0300, Michael S. Tsirkin wrote:
> On Fri, Jun 22, 2012 at 04:15:50PM -0600, Alex Williamson wrote:
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> > ---
> > 
> >  Documentation/virtual/kvm/api.txt |   17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> > index 310fe50..9b4cb2b 100644
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -1965,6 +1965,23 @@ return the hash table order in the parameter.  (If the guest is using
> >  the virtualized real-mode area (VRMA) facility, the kernel will
> >  re-create the VMRA HPTEs on the next KVM_RUN of any vcpu.)
> >  
> > +4.76 KVM_IRQFD
> > +
> > +Capability: KVM_CAP_IRQFD
> > +Architectures: x86
> > +Type: vm ioctl
> > +Parameters: struct kvm_irqfd (in)
> > +Returns: 0 on success, -1 on error
> > +
> > +Allows setting an eventfd to directly trigger a guest interrupt
> > +kvm_irqfd.fd specifies the file descriptor to use as the eventfd and
> > +kvm_irqfd.gsi specifies the irqchip pin toggled by this event.  By
> > +default this interface only supports edge triggered interrupts,
> > +meaning the specified gsi is asserted and immediately de-asserted
> > +when the eventfd is triggered.
> 
> That's a bit confusing. This assert/deassert only has effect for level.
> Do we or do we not want to maintain this assert/deassert behaviour
> for level irqfds? If yes we shouldn't say it's unsupported if
> no we should not document it.
> 
> Gleb, Avi, any thoughts?

AIUI the assert/deassert manages to work for level (I actually had vfio
injecting these for a while and it seemed to work), but I don't think it
was ever designed for level interrupts and attempting to do that is
unsupported.  Thanks,

Alex

> >  Specifying KVM_IRQFD_FLAG_DEASSIGN
> > +removes the previously set irqfd matching both kvm_irqfd.fd and
> > +kvm_irqfd.gsi.
> > +
> >  
> >  5. The kvm_run structure
> >  ------------------------



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