linux-kernel - Re: [PATCH v2 5/6] kvm: KVM

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Date:	Wed, 27 Jun 2012 08:29:04 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	avi@...hat.com, mst@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, jan.kiszka@...mens.com
Subject: Re: [PATCH v2 5/6] kvm: KVM_EOIFD, an eventfd for EOIs

On Wed, 2012-06-27 at 16:58 +0300, Gleb Natapov wrote:
> On Tue, Jun 26, 2012 at 11:10:08PM -0600, Alex Williamson wrote:
> > This new ioctl enables an eventfd to be triggered when an EOI is
> > written for a specified irqchip pin.  By default this is a simple
> > notification, but we can also tie the eoifd to a level irqfd, which
> > enables the irqchip pin to be automatically de-asserted on EOI.
> > This mode is particularly useful for device-assignment applications
> > where the unmask and notify triggers a hardware unmask.  The default
> > mode is most applicable to simple notify with no side-effects for
> > userspace usage, such as Qemu.
> > 
> > Here we make use of the reference counting of the _irq_source
> > object allowing us to share it with an irqfd and cleanup regardless
> > of the release order.
> > 
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> > ---
> > 
> >  Documentation/virtual/kvm/api.txt |   24 +++++
> >  arch/x86/kvm/x86.c                |    1 
> >  include/linux/kvm.h               |   14 +++
> >  include/linux/kvm_host.h          |   13 +++
> >  virt/kvm/eventfd.c                |  189 +++++++++++++++++++++++++++++++++++++
> >  virt/kvm/kvm_main.c               |   11 ++
> >  6 files changed, 250 insertions(+), 2 deletions(-)
> > 
> > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> > index b216709..87a2558 100644
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -1987,6 +1987,30 @@ 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.
> >  
> > +4.77 KVM_EOIFD
> > +
> > +Capability: KVM_CAP_EOIFD
> > +Architectures: x86
> > +Type: vm ioctl
> > +Parameters: struct kvm_eoifd (in)
> > +Returns: 0 on success, -1 on error
> > +
> > +KVM_EOIFD allows userspace to receive EOI notification through an
> > +eventfd for level triggered irqchip interrupts.  Behavior for edge
> > +triggered interrupts is undefined.  kvm_eoifd.fd specifies the eventfd
> Lets make it defined. EOI notification can be used by userspace to fix
> time drift due to lost interrupts. But than userspace needs to know
> which vcpu did EOI.

Hmm, do we need an additional flag and field in kvm_eoifd to filter by
vCPU then?

> Also see question below.
> 
...
> > +
> > +static int kvm_assign_eoifd(struct kvm *kvm, struct kvm_eoifd *args)
> > +{
> > +	struct eventfd_ctx *eventfd;
> > +	struct _eoifd *eoifd, *tmp;
> > +	struct _irq_source *source = NULL;
> > +
> > +	if (args->flags & KVM_EOIFD_FLAG_LEVEL_IRQFD) {
> > +		source = get_irq_source_from_irqfd(kvm, args->irqfd);
> > +		if (IS_ERR(source))
> > +			return PTR_ERR(source);
> > +	}
> > +
> Shouldn't you check that eoifd->gsi == irqfd->gsi?

Yes I should.  Thanks,

Alex


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