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Re: [Qemu-devel] [PATCH] vfio: check if host device supports INTx


From: Frank Blaschka
Subject: Re: [Qemu-devel] [PATCH] vfio: check if host device supports INTx
Date: Thu, 23 Oct 2014 10:21:40 +0200
User-agent: Mutt/1.5.17 (2007-11-01)

On Wed, Oct 22, 2014 at 11:17:11AM -0600, Alex Williamson wrote:
> On Wed, 2014-10-22 at 17:13 +0200, Frank Blaschka wrote:
> > From: Frank Blaschka <address@hidden>
> > 
> > Let the kernel announce if INTx is available. Yes, there are platforms
> > (e.g. s390) which do not support INTx.
> > 
> > Signed-off-by: Frank Blaschka <address@hidden>
> > ---
> >  hw/misc/vfio.c | 18 +++++++++++++++++-
> >  1 file changed, 17 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
> > index d66f3d2..3e9600b 100644
> > --- a/hw/misc/vfio.c
> > +++ b/hw/misc/vfio.c
> > @@ -109,6 +109,7 @@ typedef struct VFIOVGA {
> >  } VFIOVGA;
> >  
> >  typedef struct VFIOINTx {
> > +    bool available; /* intx available */
> >      bool pending; /* interrupt pending */
> >      bool kvm_accel; /* set when QEMU bypass through KVM enabled */
> >      uint8_t pin; /* which pin to pull for qemu_set_irq */
> > @@ -554,7 +555,7 @@ static int vfio_enable_intx(VFIODevice *vdev)
> >      struct vfio_irq_set *irq_set;
> >      int32_t *pfd;
> >  
> > -    if (!pin) {
> > +    if (!pin || !vdev->intx.available) {
> >          return 0;
> >      }
> >  
> > @@ -4032,6 +4033,21 @@ static int vfio_get_device(VFIOGroup *group, const 
> > char *name, VFIODevice *vdev)
> >                       vdev->host.function);
> >      }
> >  
> > +    irq_info.index = VFIO_PCI_INTX_IRQ_INDEX;
> > +    ret = ioctl(vdev->fd, VFIO_DEVICE_GET_IRQ_INFO, &irq_info);
> > +    if (ret) {
> > +        /*
> > +         * This can fail for an old kernel or legacy PCI dev
> > +         * we assume intx is available
> > +         */
> 
> Is this true?  It's unfortunately from an ABI stability standpoint that
> we weren't calling this, but the ioctl should have always been there and
> worked.  I'd rather error out here than add a fallback if this is just

ok

> paranoia.  Note that SR-IOV VFs will also report count=0 but their IRQ
> pin register will read 0.  We do also have the option to virtualize the
> IRQ pin register for s390 devices which would make them look the same as

sounds interesting, can you elaborate a little bit more on this?
At what point can we hook in and modify the pci device config space?

> an SR-IOV VF from an INTx perspective to the user.  That may be the more
> consistent option so that the VFIO IRQ INFO aligns with config space.
> Thanks,
> 
> Alex
> 
> > +        vdev->intx.available = true;
> > +        ret = 0;
> > +    } else if (irq_info.count == 0) {
> > +        vdev->intx.available = false;
> > +    } else {
> > +        vdev->intx.available = true;
> > +    }
> > +
> >  error:
> >      if (ret) {
> >          QLIST_REMOVE(vdev, next);
> 
> 
> 
> 




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