Re: [Qemu-devel] [PATCH] virtio-pci: Set the QEMU_PCI_CAP_EXPRESS capability early in its DeviceClass realize method

[Marcel Apfelbaum <marcel@redhat.com>]

On 12/01/2015 06:23 PM, Shmulik Ladkani wrote:
> In 1811e64 'hw/virtio: Add PCIe capability to virtio devices', the
> QEMU_PCI_CAP_EXPRESS capability was added to virtio's pci_dev, within
> 'virtio_pci_realize' - the pci device object realization method.
>
> This occurs to late, as 'pci_qdev_realize' (DeviceClass.realize of
> TYPE_PCI_DEVICE) has already been called, without knowing that the
> device instance is indeed an "express" instance, thus allocating
> insufficient pci config space.
>
> As a result, device may crash upon attempt to write to the PCIE config
> space.
>
> Fix, by arming the QEMU_PCI_CAP_EXPRESS capability early in virtio-pci's
> own DeviceClass realize method.
>
> This also makes code cleaner, as 'virtio_pci_realize' may now access the
> 'pci_is_express' predicate when needed.
>
> Signed-off-by: Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>
> ---
>   hw/virtio/virtio-pci.c | 24 +++++++++++++++++++-----
>   hw/virtio/virtio-pci.h |  1 +
>   2 files changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index dd48562..cee1b7b 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1814,13 +1814,10 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error **errp)
>
>       address_space_init(&proxy->modern_as, &proxy->modern_cfg, "virtio-pci-cfg-as");
>
> -    if (!(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_PCIE)
> -        && !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN)
> -        && pci_bus_is_express(pci_dev->bus)
> -        && !pci_bus_is_root(pci_dev->bus)) {
> +    if (pci_is_express(pci_dev) && pci_bus_is_express(pci_dev->bus) &&
> +        !pci_bus_is_root(pci_dev->bus)) {
>           int pos;

Hi,

Here you should check only for 'pci_is_express(pci_dev)' .


>
> -        pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;
>           pos = pcie_endpoint_cap_init(pci_dev, 0);
>           assert(pos > 0);
>
> @@ -1879,10 +1876,25 @@ static Property virtio_pci_properties[] = {
>       DEFINE_PROP_END_OF_LIST(),
>   };
>
> +static void virtio_pci_dc_realize(DeviceState *qdev, Error **errp)
> +{
> +    VirtioPCIClass *vpciklass = VIRTIO_PCI_GET_CLASS(qdev);
> +    VirtIOPCIProxy *proxy = VIRTIO_PCI(qdev);
> +    PCIDevice *pci_dev = &proxy->pci_dev;
> +
> +    if (!(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_PCIE) &&
> +        !(proxy->flags & VIRTIO_PCI_FLAG_DISABLE_MODERN)) {
> +        pci_dev->cap_present |= QEMU_PCI_CAP_EXPRESS;

And here you should also check:
      pci_bus_is_express(pci_dev->bus) && !pci_bus_is_root(pci_dev->bus))

The reason is the device becomes express only if *all* the conditions are met.

> +    }
> +
> +    vpciklass->saved_dc_realize(qdev, errp);
> +}
> +
>   static void virtio_pci_class_init(ObjectClass *klass, void *data)
>   {
>       DeviceClass *dc = DEVICE_CLASS(klass);
>       PCIDeviceClass *k = PCI_DEVICE_CLASS(klass);
> +    VirtioPCIClass *vpciklass = VIRTIO_PCI_CLASS(klass);
>
>       dc->props = virtio_pci_properties;
>       k->realize = virtio_pci_realize;
> @@ -1890,6 +1902,8 @@ static void virtio_pci_class_init(ObjectClass *klass, void *data)
>       k->vendor_id = PCI_VENDOR_ID_REDHAT_QUMRANET;
>       k->revision = VIRTIO_PCI_ABI_VERSION;
>       k->class_id = PCI_CLASS_OTHERS;
> +    vpciklass->saved_dc_realize = dc->realize;
> +    dc->realize = virtio_pci_dc_realize;
>       dc->reset = virtio_pci_reset;
>   }
>
> diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
> index ffb74bb..f18e948 100644
> --- a/hw/virtio/virtio-pci.h
> +++ b/hw/virtio/virtio-pci.h
> @@ -105,6 +105,7 @@ typedef struct {
>
>   typedef struct VirtioPCIClass {
>       PCIDeviceClass parent_class;
> +    DeviceRealize saved_dc_realize;

I would change the name to parent_realize :)

Also please add "for-2.5" to prefix.

Thanks for posting it!
Marcel

>       void (*realize)(VirtIOPCIProxy *vpci_dev, Error **errp);
>   } VirtioPCIClass;
>
>