Re: [PATCH] hw/pci/pcie: Move hot plug capability check to pre_plug callback

[Julia Suvorova]

On Tue, Jun 2, 2020 at 5:54 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Mon, Jun 01, 2020 at 06:29:34PM +0200, Julia Suvorova wrote:
> > Check for hot plug capability earlier to avoid removing devices attached
> > during the initialization process.
> >
> > Run qemu with an unattached drive:
> >   -drive file=$FILE,if=none,id=drive0 \
> >   -device pcie-root-port,id=rp0,slot=3,bus=pcie.0,hotplug=off
> > Hotplug a block device:
> >   device_add virtio-blk-pci,id=blk0,drive=drive0,bus=rp0
> > If hotplug fails on plug_cb, drive0 will be deleted.
> >
> > Signed-off-by: Julia Suvorova <jusual@redhat.com>
>
>
> Fixes: 0501e1aa1d32a6 ("hw/pci/pcie: Forbid hot-plug if it's disabled on the 
> slot")
>
> correct?

Yes.

> > ---
> > Hard to say if it's a bug or generally acceptable behaviour, but seems like
> > hotplug_handler_plug should never fail.
> >
> >  hw/pci/pcie.c | 19 +++++++++++--------
> >  1 file changed, 11 insertions(+), 8 deletions(-)
> >
> > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> > index f50e10b8fb..5b9c022d91 100644
> > --- a/hw/pci/pcie.c
> > +++ b/hw/pci/pcie.c
> > @@ -407,6 +407,17 @@ static void pcie_cap_slot_plug_common(PCIDevice 
> > *hotplug_dev, DeviceState *dev,
> >  void pcie_cap_slot_pre_plug_cb(HotplugHandler *hotplug_dev, DeviceState 
> > *dev,
> >                                 Error **errp)
> >  {
> > +    PCIDevice *hotplug_pdev = PCI_DEVICE(hotplug_dev);
> > +    uint8_t *exp_cap = hotplug_pdev->config + hotplug_pdev->exp.exp_cap;
> > +    uint32_t sltcap = pci_get_word(exp_cap + PCI_EXP_SLTCAP);
> > +
> > +    /* Check if hot-plug is disabled on the slot */
> > +    if (dev->hotplugged && (sltcap & PCI_EXP_SLTCAP_HPC) == 0) {
> > +        error_setg(errp, "Hot-plug failed: unsupported by the port device 
> > '%s'",
> > +                         DEVICE(hotplug_pdev)->id);
> > +        return;
> > +    }
> > +
> >      pcie_cap_slot_plug_common(PCI_DEVICE(hotplug_dev), dev, errp);
> >  }
> >
> > @@ -415,7 +426,6 @@ void pcie_cap_slot_plug_cb(HotplugHandler *hotplug_dev, 
> > DeviceState *dev,
> >  {
> >      PCIDevice *hotplug_pdev = PCI_DEVICE(hotplug_dev);
> >      uint8_t *exp_cap = hotplug_pdev->config + hotplug_pdev->exp.exp_cap;
> > -    uint32_t sltcap = pci_get_word(exp_cap + PCI_EXP_SLTCAP);
> >      PCIDevice *pci_dev = PCI_DEVICE(dev);
> >
> >      /* Don't send event when device is enabled during qemu machine 
> > creation:
> > @@ -431,13 +441,6 @@ void pcie_cap_slot_plug_cb(HotplugHandler 
> > *hotplug_dev, DeviceState *dev,
> >          return;
> >      }
> >
> > -    /* Check if hot-plug is disabled on the slot */
> > -    if ((sltcap & PCI_EXP_SLTCAP_HPC) == 0) {
> > -        error_setg(errp, "Hot-plug failed: unsupported by the port device 
> > '%s'",
> > -                         DEVICE(hotplug_pdev)->id);
> > -        return;
> > -    }
> > -
> >      /* To enable multifunction hot-plug, we just ensure the function
> >       * 0 added last. When function 0 is added, we set the sltsta and
> >       * inform OS via event notification.
> > --
> > 2.25.4
>