On Thu, 2012-06-28 at 11:29 +0300, Michael S. Tsirkin wrote: > On Wed, Jun 27, 2012 at 09:52:52PM -0600, Alex Williamson wrote: > > On Thu, 2012-06-28 at 01:28 +0300, Michael S. Tsirkin wrote: > > > On Wed, Jun 27, 2012 at 03:28:19PM -0600, Alex Williamson wrote: > > > > On Thu, 2012-06-28 at 00:14 +0300, Michael S. Tsirkin wrote: > > > > > On Wed, Jun 27, 2012 at 02:59:09PM -0600, Alex Williamson wrote: > > > > > > 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@xxxxxxxxxx> > > > > > > > > --- > > > > > > > > > > > > > > > > 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 > > > > > > > > > > Fragile? If you set eventfd as LEVEL but GSI is really edge then > > > > > it all explodes, right? So why give users the option to shoot > > > > > themselves in the foot? > > > > > > > > If the guest has the ioapic rte set to edge at the time I call KVM_IRQFD > > > > to register my level interrupt then it all explodes, right? I'd rather > > > > let the user shoot themselves than play Russian roulette with the guest. > > > > Am I misunderstanding what you mean by looking that the GSI to see if > > > > it's level or edge? > > > > > > Not sure. > > > I simply mean this: if eventfd is bound to irqfd, set level from irqfd > > > and clear from eventfd ack notifier. > > > > Are you simply saying assert (kvm_set_irq(,,,1)) from irqfd trigger and > > de-assert (kvm_set_irq(,,,0)) from eventfd ack notifier (aka KVM_EOIFD)? > > Yes. > > > > There's no need for a special IRQ_LEVEL for this. > > > > That ignores the whole problem of when do we need to allocate a new > > irq_source_id and when do we inject using KVM_USERSPACE_IRQ_SOURCE_ID. > > We've already discussed that a level triggered, externally fired > > interrupt must use a separate source ID from Qemu userspace. Therefore > > when you say "look at the GSI to see if it's level or edge", I assume > > you mean trace the gsi back to the pic/ioapic pin and look at the > > trigger mode. That trigger mode is configured by the guest, so that > > means that at the point in time when we call KVM_IRQFD we make a > > determination based on how the _guest_ has programmed the ioapic. That > > may not match the interrupt we expect to inject. On the other hand, the > > user calling KVM_IRQFD absolutely knows the type of interrupt provided > > by their device. I think we need a flag regardless of whether your > > patch is accepted. We may be able to share the inject handler if it is > > accepted, but it doesn't change the user API. Thanks, > > > > Alex > > This has merit, I am just looking for a way out > without adding LEVEL flag which seems to duplicate > what guest does, especially now it turns out > we can't add new flags to IRQFD. This hasn't been decided yet AFAICT. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
