Re: [Qemu-devel] [PATCH 1/2] VFIO-AER: Vfio-pci driver changes for supporting AER

[Alex Williamson]

On Fri, 2013-01-11 at 08:45 +0000, Pandarathil, Vijaymohan R wrote:
> 
> > -----Original Message-----
> > From: Alex Williamson [mailto:address@hidden
> > Sent: Wednesday, January 09, 2013 11:05 AM
> > To: Pandarathil, Vijaymohan R
> > Cc: Bjorn Helgaas; Gleb Natapov; address@hidden; qemu-
> > address@hidden; address@hidden; address@hidden
> > Subject: Re: [PATCH 1/2] VFIO-AER: Vfio-pci driver changes for supporting
> > AER
> > 
> > On Wed, 2013-01-09 at 10:52 -0700, Alex Williamson wrote:
> > > On Wed, 2013-01-09 at 06:26 +0000, Pandarathil, Vijaymohan R wrote:
> > > >         - New ioctl which is used to pass the eventfd that is signaled 
> > > > when
> > > >           an error occurs in the vfio_pci_device
> > > >
> > > >         - Register pci_error_handler for the vfio_pci driver
> > > >
> > > >         - When the device encounters an error, the error handler 
> > > > registered
> > by
> > > >           the vfio_pci driver gets invoked by the AER infrastructure
> > > >
> > > >         - In the error handler, signal the eventfd registered for the 
> > > > device.
> > > >
> > > >         - This results in the qemu eventfd handler getting invoked and
> > > >           appropriate action taken for the guest.
> > > >
> > > > Signed-off-by: Vijay Mohan Pandarathil <address@hidden>
> > > > ---
> > > >  drivers/vfio/pci/vfio_pci.c         | 29 +++++++++++++++++++++++++++++
> > > >  drivers/vfio/pci/vfio_pci_private.h |  1 +
> > > >  drivers/vfio/vfio.c                 |  8 ++++++++
> > > >  include/linux/vfio.h                |  1 +
> > > >  include/uapi/linux/vfio.h           |  9 +++++++++
> > > >  5 files changed, 48 insertions(+)
> > > >
> > > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > > > index 6c11994..4ae9526 100644
> > > > --- a/drivers/vfio/pci/vfio_pci.c
> > > > +++ b/drivers/vfio/pci/vfio_pci.c
> > > > @@ -207,6 +207,8 @@ static long vfio_pci_ioctl(void *device_data,
> > > >                 if (vdev->reset_works)
> > > >                         info.flags |= VFIO_DEVICE_FLAGS_RESET;
> > > >
> > > > +               info.flags |= VFIO_DEVICE_FLAGS_AER_NOTIFY;
> > > > +
> > >
> > > This appears to be a PCI specific flag, so the name should include
> > > _PCI_.  We also support non-PCIe devices and it seems like it would be
> > > possible to not have AER support available, so shouldn't this be
> > > conditional?
> 
> Will do that.
> 
> > >
> > > >                 info.num_regions = VFIO_PCI_NUM_REGIONS;
> > > >                 info.num_irqs = VFIO_PCI_NUM_IRQS;
> > > >
> > > > @@ -348,6 +350,19 @@ static long vfio_pci_ioctl(void *device_data,
> > > >
> > > >                 return ret;
> > > >
> > > > +       } else if (cmd == VFIO_DEVICE_SET_ERRFD) {
> > > > +               int32_t fd = (int32_t)arg;
> > > > +
> > > > +               if (fd < 0)
> > > > +                       return -EINVAL;
> > > > +
> > > > +               vdev->err_trigger = eventfd_ctx_fdget(fd);
> > > > +
> > > > +               if (IS_ERR(vdev->err_trigger))
> > > > +                       return PTR_ERR(vdev->err_trigger);
> > > > +
> > > > +               return 0;
> > > > +
> > >
> > > I'm not sure why we wouldn't describe this as just another interrupt
> > > from the device and configure it via SET_IRQ.  This ioctl has very
> > > limited use and doesn't follow any of the conventions of all the other
> > > vfio ioctls.
> 
> I thought this was a fairly simple ioctl to implement this way. Moreover, 
> there is no device interrupt involved. Let me know if you really want to 
> model it as a SET_IRQ ioctl.

I'd like to see something else for sure.  We're trying to do AER
piecemeal but this ioctl leaves no room for anything else.  Seems like a
soon to be wasted ioctl number.  Note that there isn't even a de-assign
interface, nor a flag to set to indicate de-assignment.  The SET_IRQ
ioctl already handles these in a very similar way to how we'd want to
handle it for error signaling.  It doesn't seem like that much of a
stretch to me to include it there, but I'd also entertain other ideas.
Thanks,

Alex

> > >
> > > >         } else if (cmd == VFIO_DEVICE_RESET)
> > > >                 return vdev->reset_works ?
> > > >                         pci_reset_function(vdev->pdev) : -EINVAL;
> > > > @@ -527,11 +542,25 @@ static void vfio_pci_remove(struct pci_dev *pdev)
> > > >         kfree(vdev);
> > > >  }
> > > >
> > > > +static pci_ers_result_t vfio_err_detected(struct pci_dev *pdev,
> > > > +                               pci_channel_state_t state)
> > > > +{
> > > > +       struct vfio_pci_device *vdev = vfio_get_vdev(&pdev->dev);
> > > > +
> > > > +       eventfd_signal(vdev->err_trigger, 1);
> > > > +       return PCI_ERS_RESULT_CAN_RECOVER;
> > > > +}
> > >
> > > What if err_trigger hasn't been set?
> 
> Will fix that.
> 
> > >
> > > > +
> > > > +static const struct pci_error_handlers vfio_err_handlers = {
> > > > +       .error_detected = vfio_err_detected,
> > > > +};
> > > > +
> > > >  static struct pci_driver vfio_pci_driver = {
> > > >         .name           = "vfio-pci",
> > > >         .id_table       = NULL, /* only dynamic ids */
> > > >         .probe          = vfio_pci_probe,
> > > >         .remove         = vfio_pci_remove,
> > > > +       .err_handler    = &vfio_err_handlers,
> > > >  };
> > > >
> > > >  static void __exit vfio_pci_cleanup(void)
> > > > diff --git a/drivers/vfio/pci/vfio_pci_private.h
> > b/drivers/vfio/pci/vfio_pci_private.h
> > > > index 611827c..daee62f 100644
> > > > --- a/drivers/vfio/pci/vfio_pci_private.h
> > > > +++ b/drivers/vfio/pci/vfio_pci_private.h
> > > > @@ -55,6 +55,7 @@ struct vfio_pci_device {
> > > >         bool                    bardirty;
> > > >         struct pci_saved_state  *pci_saved_state;
> > > >         atomic_t                refcnt;
> > > > +       struct eventfd_ctx      *err_trigger;
> > > >  };
> > > >
> > > >  #define is_intx(vdev) (vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX)
> > > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> > > > index 56097c6..5ed5a54 100644
> > > > --- a/drivers/vfio/vfio.c
> > > > +++ b/drivers/vfio/vfio.c
> > > > @@ -693,6 +693,14 @@ void *vfio_del_group_dev(struct device *dev)
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(vfio_del_group_dev);
> > > >
> > > > +void *vfio_get_vdev(struct device *dev)
> > > > +{
> > > > +       struct vfio_device *device = dev_get_drvdata(dev);
> > > > +
> > > > +       return device->device_data;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(vfio_get_vdev);
> > > > +
> > >
> > > This is unsafe.  How do we know dev is a vfio device?  How do we keep
> > > that drvdata valid while you're using it?  I think you want to export
> > > the existing vfio_group_get_device() and vfio_device_put().  Thanks,
> > 
> > vfio_group_get_device() isn't quite what you want either since it
> > assumes a reference count on the group.  You'll want something like
> > vfio_add_group_dev() or vfio_dev_present(), perhaps moving the
> > iommu_group_get -> vfio_group_get_from_iommu -> vfio_group_get_device
> > into a helper function.  Thanks,
> 
> Thanks for the pointers. Will make the change.
> 
> Vijay
> 
> > 
> > Alex
> > 
> > > >  /**
> > > >   * VFIO base fd, /dev/vfio/vfio
> > > >   */
> > > > diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> > > > index ab9e862..3c97b03 100644
> > > > --- a/include/linux/vfio.h
> > > > +++ b/include/linux/vfio.h
> > > > @@ -45,6 +45,7 @@ extern int vfio_add_group_dev(struct device *dev,
> > > >                               void *device_data);
> > > >
> > > >  extern void *vfio_del_group_dev(struct device *dev);
> > > > +extern void *vfio_get_vdev(struct device *dev);
> > > >
> > > >  /**
> > > >   * struct vfio_iommu_driver_ops - VFIO IOMMU driver callbacks
> > > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > > > index 4758d1b..fa67213 100644
> > > > --- a/include/uapi/linux/vfio.h
> > > > +++ b/include/uapi/linux/vfio.h
> > > > @@ -147,6 +147,7 @@ struct vfio_device_info {
> > > >         __u32   flags;
> > > >  #define VFIO_DEVICE_FLAGS_RESET        (1 << 0)        /* Device 
> > > > supports
> > reset */
> > > >  #define VFIO_DEVICE_FLAGS_PCI  (1 << 1)        /* vfio-pci device */
> > > > +#define VFIO_DEVICE_FLAGS_AER_NOTIFY (1 << 2)  /* Supports aer
> > notify */
> > > >         __u32   num_regions;    /* Max region index + 1 */
> > > >         __u32   num_irqs;       /* Max IRQ index + 1 */
> > > >  };
> > > > @@ -288,6 +289,14 @@ struct vfio_irq_set {
> > > >   */
> > > >  #define VFIO_DEVICE_RESET              _IO(VFIO_TYPE, VFIO_BASE + 11)
> > > >
> > > > +/**
> > > > + * VFIO_DEVICE_SET_ERRFD - _IO(VFIO_TYPE, VFIO_BASE + 12)
> > > > + *
> > > > + * Pass the eventfd to the vfio-pci driver for signalling any device
> > > > + * error notifications
> > > > + */
> > > > +#define VFIO_DEVICE_SET_ERRFD          _IO(VFIO_TYPE, VFIO_BASE + 12)
> > > > +
> > > >  /*
> > > >   * The VFIO-PCI bus driver makes use of the following fixed region and
> > > >   * IRQ index mapping.  Unimplemented regions return a size of zero.
> > >
> > >
> > 
> > 
>