Re: [PATCHv4 2/2] kvm: deliver msi interrupts from irq handler

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 28, 2012 at 01:43:34PM +0200, Gleb Natapov wrote:
> On Wed, Oct 17, 2012 at 06:06:06PM +0200, Michael S. Tsirkin wrote:
> > We can deliver certain interrupts, notably MSI,
> > from atomic context.  Use kvm_set_irq_inatomic,
> > to implement an irq handler for msi.
> > 
> > This reduces the pressure on scheduler in case
> > where host and guest irq share a host cpu.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  virt/kvm/assigned-dev.c | 36 ++++++++++++++++++++++++++----------
> >  1 file changed, 26 insertions(+), 10 deletions(-)
> > 
> > diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> > index 23a41a9..3642239 100644
> > --- a/virt/kvm/assigned-dev.c
> > +++ b/virt/kvm/assigned-dev.c
> > @@ -105,6 +105,15 @@ static irqreturn_t kvm_assigned_dev_thread_intx(int irq, void *dev_id)
> >  }
> >  
> >  #ifdef __KVM_HAVE_MSI
> > +static irqreturn_t kvm_assigned_dev_msi(int irq, void *dev_id)
> > +{
> > +	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > +	int ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> > +				       assigned_dev->irq_source_id,
> > +				       assigned_dev->guest_irq, 1);
> Why not use kvm_set_msi_inatomic() and drop kvm_set_irq_inatomic() from
> previous patch? 

kvm_set_msi_inatomic needs a routing entry, and
we don't have the routing entry at this level.

Further, guest irq might not be an MSI: host MSI
can cause guest intx injection I think, we need to
bounce it to thread as we did earlier.

> > +	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> > +}
> > +
> >  static irqreturn_t kvm_assigned_dev_thread_msi(int irq, void *dev_id)
> >  {
> >  	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > @@ -117,6 +126,23 @@ static irqreturn_t kvm_assigned_dev_thread_msi(int irq, void *dev_id)
> >  #endif
> >  
> >  #ifdef __KVM_HAVE_MSIX
> > +static irqreturn_t kvm_assigned_dev_msix(int irq, void *dev_id)
> > +{
> > +	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > +	int index = find_index_from_host_irq(assigned_dev, irq);
> > +	u32 vector;
> > +	int ret = 0;
> > +
> > +	if (index >= 0) {
> > +		vector = assigned_dev->guest_msix_entries[index].vector;
> > +		ret = kvm_set_irq_inatomic(assigned_dev->kvm,
> > +					   assigned_dev->irq_source_id,
> > +					   vector, 1);
> > +	}
> > +
> > +	return unlikely(ret == -EWOULDBLOCK) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
> > +}
> > +
> >  static irqreturn_t kvm_assigned_dev_thread_msix(int irq, void *dev_id)
> >  {
> >  	struct kvm_assigned_dev_kernel *assigned_dev = dev_id;
> > @@ -334,11 +360,6 @@ static int assigned_device_enable_host_intx(struct kvm *kvm,
> >  }
> >  
> >  #ifdef __KVM_HAVE_MSI
> > -static irqreturn_t kvm_assigned_dev_msi(int irq, void *dev_id)
> > -{
> > -	return IRQ_WAKE_THREAD;
> > -}
> > -
> >  static int assigned_device_enable_host_msi(struct kvm *kvm,
> >  					   struct kvm_assigned_dev_kernel *dev)
> >  {
> > @@ -363,11 +384,6 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
> >  #endif
> >  
> >  #ifdef __KVM_HAVE_MSIX
> > -static irqreturn_t kvm_assigned_dev_msix(int irq, void *dev_id)
> > -{
> > -	return IRQ_WAKE_THREAD;
> > -}
> > -
> >  static int assigned_device_enable_host_msix(struct kvm *kvm,
> >  					    struct kvm_assigned_dev_kernel *dev)
> >  {
> > -- 
> > MST
> > --
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> 
> --
> 			Gleb.