Re: [PATCHv3 RFC 1/2] kvm: implement kvm_set_msi_inatomic

[Gleb Natapov <gleb@redhat.com>]

On Wed, Jun 13, 2012 at 06:59:50PM +0300, Michael S. Tsirkin wrote:
> On Wed, Jun 13, 2012 at 04:01:24PM +0300, Gleb Natapov wrote:
> > On Mon, Jun 11, 2012 at 02:19:22PM +0300, Michael S. Tsirkin wrote:
> > > We do not want a potential broadcast to all VCPUs to run in
> > > a host IRQ handler. Implement an API that sends an MSI
> > > interrupt but only if it's safe from interrupt context,
> > > that is if it is a unicast.
> > > 
> > We will still iterate over all vcpus, we may as well deliver to them. Or
> > you want to avoid a lot of vcpu kicks?
> 
> This is an intermediate stage (thus RFC) for adding a cache:
> we can't cache if it's a broadcast.
> 
You skipped my comment about the code  bellow :)

> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > ---
> > >  include/linux/kvm_host.h |  2 ++
> > >  virt/kvm/irq_comm.c      | 37 ++++++++++++++++++++++++++++++++-----
> > >  2 files changed, 34 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index c446435..ddb476a 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -618,6 +618,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
> > >  int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level);
> > >  int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
> > >  		int irq_source_id, int level);
> > > +int kvm_set_msi_inatomic(struct kvm_kernel_irq_routing_entry *irq_entry,
> > > +			 struct kvm *kvm);
> > >  void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
> > >  void kvm_register_irq_ack_notifier(struct kvm *kvm,
> > >  				   struct kvm_irq_ack_notifier *kian);
> > > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> > > index 5afb431..3395e03 100644
> > > --- a/virt/kvm/irq_comm.c
> > > +++ b/virt/kvm/irq_comm.c
> > > @@ -114,13 +114,20 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
> > >  	return r;
> > >  }
> > >  
> > > -int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
> > > -		struct kvm *kvm, int irq_source_id, int level)
> > > +static bool kvm_msi_is_multicast(unsigned dest, int dest_mode)
> > >  {
> > > -	struct kvm_lapic_irq irq;
> > > +	if (dest_mode == 0)
> > > +		/* Physical mode. */
> > > +		return dest == 0xff;
> > > +	else
> > > +		/* Logical mode. */
> > > +		return dest & (dest - 1);
> > > +}
> > >  
> > > -	if (!level)
> > > -		return -1;
> > > +static int __kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
> > > +			 struct kvm *kvm, bool noblock)
> > > +{
> > > +	struct kvm_lapic_irq irq;
> > >  
> > >  	trace_kvm_msi_set_irq(e->msi.address_lo, e->msi.data);
> > >  
> > > @@ -134,10 +141,30 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
> > >  	irq.level = 1;
> > >  	irq.shorthand = 0;
> > >  
> > > +	/* Multicast MSI doesn't really block but might take a long time. */
> > > +	if (unlikely(noblock && kvm_msi_is_multicast(irq.dest_id,
> > > +						     irq.delivery_mode)))
> > delivery_mode? Should be dest_mode. But you probably need to check that
> > delivery_mode is not ExtINT either.
> > 
> > > +		return -EWOULDBLOCK;
> > > +
> > >  	/* TODO Deal with RH bit of MSI message address */
> > >  	return kvm_irq_delivery_to_apic(kvm, NULL, &irq);
> > >  }
> > >  
> > > +int kvm_set_msi_inatomic(struct kvm_kernel_irq_routing_entry *e,
> > > +			 struct kvm *kvm)
> > > +{
> > > +	return __kvm_set_msi(e, kvm, true);
> > > +}
> > > +
> > > +int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
> > > +			 struct kvm *kvm, int irq_source_id, int level)
> > > +{
> > > +	if (unlikely(!level))
> > > +		return -1;
> > > +
> > > +	return __kvm_set_msi(e, kvm, false);
> > > +}
> > > +
> > >  int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi)
> > >  {
> > >  	struct kvm_kernel_irq_routing_entry route;
> > > -- 
> > > MST
> > > 
> > > --
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> > 
> > --
> > 			Gleb.

--
			Gleb.