lkml.org 
[lkml]   [2012]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2 4/6] kvm: Extend irqfd to support level interrupts
From
Date
On Wed, 2012-06-27 at 12:51 +0300, Michael S. Tsirkin wrote:
> On Tue, Jun 26, 2012 at 11:09:46PM -0600, Alex Williamson wrote:
> > In order to inject an interrupt from an external source using an
> > irqfd, we need to allocate a new irq_source_id. This allows us to
> > assert and (later) de-assert an interrupt line independently from
> > users of KVM_IRQ_LINE and avoid lost interrupts.
> >
> > We also add what may appear like a bit of excessive infrastructure
> > around an object for storing this irq_source_id. However, notice
> > that we only provide a way to assert the interrupt here. A follow-on
> > interface will make use of the same irq_source_id to allow de-assert.
> >
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > ---
> >
> > Documentation/virtual/kvm/api.txt | 5 ++
> > arch/x86/kvm/x86.c | 1
> > include/linux/kvm.h | 3 +
> > virt/kvm/eventfd.c | 95 +++++++++++++++++++++++++++++++++++--
> > 4 files changed, 99 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> > index ea9edce..b216709 100644
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -1981,6 +1981,11 @@ the guest using the specified gsi pin. The irqfd is removed using
> > the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd
> > and kvm_irqfd.gsi.
> >
> > +With KVM_IRQFD_FLAG_LEVEL KVM_IRQFD allocates a new IRQ source ID for
> > +the requested irqfd. This is necessary to share level triggered
> > +interrupts with those injected through KVM_IRQ_LINE. IRQFDs created
> > +with KVM_IRQFD_FLAG_LEVEL must also set this flag when de-assiging.
> > +KVM_IRQFD_FLAG_LEVEL support is indicated by KVM_CAP_IRQFD_LEVEL.
>
> Note that if my patch removing auto-deassert gets accepted,
> this is not needed at all: we can just look at the GSI
> to see if it's level or edge.

I'm not sure this is a good idea. I know from vfio that I'm injecting a
level interrupt regardless of how the guest has the pic/ioapic
programmed at the time I'm calling this ioctl. Peeking across address
spaces to get to the right pin on the right pic/ioapic and see how it's
currently programmed seems fragile. Thanks,

Alex



\
 
 \ /
  Last update: 2012-06-27 23:21    [W:0.149 / U:0.192 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site