Re: [PATCH v6 13/15] hw/pci: Determine if rombar is explicitly enabled

[Markus Armbruster <armbru@redhat.com>]

Akihiko Odaki <akihiko.odaki@daynix.com> writes:

> vfio determines if rombar is explicitly enabled by inspecting QDict.
> Inspecting QDict is not nice because QDict is untyped and depends on the
> details on the external interface. Add an infrastructure to determine if
> rombar is explicitly enabled to hw/pci.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>  include/hw/pci/pci_device.h | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/include/hw/pci/pci_device.h b/include/hw/pci/pci_device.h
> index ca151325085d..c4fdc96ef50d 100644
> --- a/include/hw/pci/pci_device.h
> +++ b/include/hw/pci/pci_device.h
> @@ -205,6 +205,11 @@ static inline uint16_t pci_get_bdf(PCIDevice *dev)
>      return PCI_BUILD_BDF(pci_bus_num(pci_get_bus(dev)), dev->devfn);
>  }
>  
> +static inline bool pci_rom_bar_explicitly_enabled(PCIDevice *dev)
> +{
> +    return dev->rom_bar && dev->rom_bar != -1;

Compares signed with unsigned: rom_bar is uint32_t, -1 is int.

If int is at most 32 bits, the comparison converts -1 to
(uint32_t)0xffffffff.

If int is wider, it converts dev->rom_bar to int without changing its
value.  In particular, it converts the default value 0xffffffff (written
as -1 in the previous patch) to (int)0xffffffff.  Oops.

Best not to mix signed and unsigned in comparisons.  Easy enough to
avoid here.

Still, we don't actually test "rom_bar has not been set".  We test
"rom_bar has the default value".  Nothing stops a user from passing
rombar=0xffffffff to -device.  See my review of the next patch.

> +}
> +
>  static inline void pci_set_power(PCIDevice *pci_dev, bool state)
>  {
>      /*