Re: [Qemu-devel] [PATCH] pci: Don't deliver MSI/MSI-X messages if bus master support is off

["Michael S. Tsirkin" <mst@redhat.com>]

On Sat, Jul 19, 2014 at 06:55:48PM +0200, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
> 
> The spec says (and real HW confirms this) that, if the bus master bit
> is 0, the device will not generate any PCI accesses. MSI and MSI-X
> messages fall among these.
> 
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

I guess an alternative is for callers to check before
invoking msi_notify. Please note is this is only option
when using e.g. irqfd, so this has some advantages.
Is there a specific device that is affected by this?
I would expect drivers to disable msi before clearing
bus master bit ...

> ---
>  hw/pci/msi.c  | 4 ++++
>  hw/pci/msix.c | 4 ++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/hw/pci/msi.c b/hw/pci/msi.c
> index a4a3040..36b651b 100644
> --- a/hw/pci/msi.c
> +++ b/hw/pci/msi.c
> @@ -285,6 +285,10 @@ void msi_notify(PCIDevice *dev, unsigned int vector)
>          return;
>      }
>  
> +    if (!(pci_get_word(dev->config + PCI_COMMAND) & PCI_COMMAND_MASTER)) {
> +        return;
> +    }
> +
>      msg = msi_get_message(dev, vector);
>  
>      MSI_DEV_PRINTF(dev,
> diff --git a/hw/pci/msix.c b/hw/pci/msix.c
> index 5c49bfc..c77ae7d 100644
> --- a/hw/pci/msix.c
> +++ b/hw/pci/msix.c
> @@ -437,6 +437,10 @@ void msix_notify(PCIDevice *dev, unsigned vector)
>          return;
>      }
>  
> +    if (!(pci_get_word(dev->config + PCI_COMMAND) & PCI_COMMAND_MASTER)) {
> +        return;
> +    }
> +
>      msg = msix_get_message(dev, vector);
>  
>      stl_le_phys(&address_space_memory, msg.address, msg.data);
> -- 
> 1.8.1.1.298.ge7eed54
>