Re: [Xen-devel] [PATCH] xen: xen-pciback: Reset MSI-X state when exposing a device

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.12.18 at 03:19, <chao.gao@xxxxxxxxx> wrote:
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -87,6 +87,55 @@ static struct pcistub_device *pcistub_device_alloc(struct 
> pci_dev *dev)
>       return psdev;
>  }
>  
> +/*
> + * Reset Xen internal MSI-X state by invoking PHYSDEVOP_{release, 
> prepare}_msix.
> + */
> +int pcistub_msix_reset(struct pci_dev *dev)
> +{
> +#ifdef CONFIG_PCI_MSI
> +     if (dev->msix_cap) {
> +             struct physdev_pci_device ppdev = {
> +                     .seg = pci_domain_nr(dev->bus),
> +                     .bus = dev->bus->number,
> +                     .devfn = dev->devfn
> +             };
> +             int err;
> +             u16 val;
> +
> +             /*
> +              * Do a write first to flush Xen's internal state to hardware
> +              * such that the following read can infer whether MSI-X maskall
> +              * bit is set by Xen.
> +              */
> +             pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &val);
> +             pci_write_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, val);
> +
> +             pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &val);
> +             if (!(val & PCI_MSIX_FLAGS_MASKALL))
> +                     return 0;

I'm agreeing with prior comments: I don't see why you need
this conditional.

> +             pr_info("Reset MSI-X state for device %04x:%02x:%02x.%d\n",
> +                     ppdev.seg, ppdev.bus, PCI_SLOT(ppdev.devfn),
> +                     PCI_FUNC(ppdev.devfn));
> +
> +             err = HYPERVISOR_physdev_op(PHYSDEVOP_release_msix, &ppdev);
> +             if (err) {
> +                     dev_warn(&dev->dev, "MSI-X release failed (%d)\n",
> +                              err);
> +                     return err;
> +             }
> +
> +             err = HYPERVISOR_physdev_op(PHYSDEVOP_prepare_msix, &ppdev);
> +             if (err) {
> +                     dev_err(&dev->dev, "MSI-X preparation failed (%d)\n",
> +                             err);

Please can you make both log messages distinguishable from
the pre-existing ones, to aid diagnosis of possible probelms?

Jan



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