Re: [PATCH 5/5] KVM: s390: clear_io_irq() requests are not expected for adapter interrupts

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 8 Nov 2017 12:04:22 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 11/08/2017 10:19 AM, Cornelia Huck wrote:
> > On Wed,  8 Nov 2017 09:41:43 +0100
> > Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >   
> >> From: Michael Mueller <mimu@linux.vnet.ibm.com>
> >>
> >> There is a chance to delete not yet delivered I/O interrupts if an
> >> exploiter uses the subsystem identification word 0x0000 while
> >> processing a KVM_DEV_FLIC_CLEAR_IO_IRQ ioctl. -EINVAL will be returned
> >> now instead in that case.
> >>
> >> Classic interrupts will always have bit 0x10000 set in the schid while
> >> adapter interrupts have a zero schid. The clear_io_irq interface is
> >> only useful for classic interrupts (as adapter interrupts belong to
> >> many devices). Let's make this interface more strict and forbid a schid
> >> of 0.  
> > 
> > I'm wondering: Is there any possible use case to clear adapter
> > interrupts? This interface was introduced to handle the case where a
> > CRW was made pending for a subchannel (which implies any pending
> > interrupt needs to be cleared.)  
> 
> The problem with clearing adapter interrupts is that is actually a summary
> interrupt for every potential device. So I somewhat consider an adapter interrupt
> pending when the summary indicator went from 0 to 1. So I dont think clearing
> a single one makes not much sense. (And this interface would be wrong for
> that I think)

Yes, this interface would be problematic. I'm not sure what's supposed
to happen with crws vs. pending adapter interrupts, though.

> The only use cases I can imagine for clearing adapter interrupts (e.g. reset)
> is already covered by KVM_DEV_FLIC_CLEAR_IRQS
> 
> > 
> > Alas, I cannot check the adapter interrupt question myself, as the
> > public doc is lacking :( But qdio as another adapter interrupt user
> > comes to mind (not that we support it in qemu, but still...)
> >   
> >>
> >> Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
> >> Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
> >> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> >> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> >> ---
> >>  Documentation/virtual/kvm/devices/s390_flic.txt | 3 +++
> >>  arch/s390/kvm/interrupt.c                       | 2 ++
> >>  2 files changed, 5 insertions(+)
> >>
> >> diff --git a/Documentation/virtual/kvm/devices/s390_flic.txt b/Documentation/virtual/kvm/devices/s390_flic.txt
> >> index 2f1cbf1..27ad53c 100644
> >> --- a/Documentation/virtual/kvm/devices/s390_flic.txt
> >> +++ b/Documentation/virtual/kvm/devices/s390_flic.txt
> >> @@ -156,3 +156,6 @@ FLIC with an unknown group or attribute gives the error code EINVAL (instead of
> >>  ENXIO, as specified in the API documentation). It is not possible to conclude
> >>  that a FLIC operation is unavailable based on the error code resulting from a
> >>  usage attempt.
> >> +
> >> +Note: The KVM_DEV_FLIC_CLEAR_IO_IRQ ioctl will return EINVAL in case a zero
> >> +schid is specified.
> >> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> >> index a3da4f3..c8aacce 100644
> >> --- a/arch/s390/kvm/interrupt.c
> >> +++ b/arch/s390/kvm/interrupt.c
> >> @@ -2191,6 +2191,8 @@ static int clear_io_irq(struct kvm *kvm, struct kvm_device_attr *attr)
> >>  		return -EINVAL;
> >>  	if (copy_from_user(&schid, (void __user *) attr->addr, sizeof(schid)))
> >>  		return -EFAULT;
> >> +	if (!schid)
> >> +		return -EINVAL;
> >>  	kfree(kvm_s390_get_io_int(kvm, isc_mask, schid));
> >>  	/*
> >>  	 * If userspace is conforming to the architecture, we can have at most  
> >   
> 

As this particular interface would not be a good match for whatever we
need to do for adapter interrupts, let's go with this patch.

Reviewed-by: Cornelia Huck <cohuck@redhat.com>