Hi Alex, Thanks for your reply. On Wed, Apr 8, 2015 at 8:17 AM, Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > Hi Wei, > > On Tue, 2015-04-07 at 21:02 -0700, Wei Hu wrote: >> Hi Alex, >> >> With your change "Release devices with BusMaster disabled", I've found >> that my VFIO device driver is no longer receiving MSI interrupts. >> After reviewing the code I think it makes sense. But I had two >> questions below while debugging my issue. >> >> 1. If I had set the bus master bit in the command register by hand >> before opening the vfio device, the kernel would actually leave >> BusMaster enabled. This seems to contradict the call to >> pci_clear_master() from vfio_pci_enable(). What's going on here, is >> something else enabling BusMaster? > > I don't see this behavior. If I use a test program that simply opens > the vfio group, configures the IOMMU container and gets a device file > descriptor, BusMaster is clear at that point regardless of whether the > device has it enabled or disabled beforehand. Are you perhaps attaching > bridges to vfio-pci and the bridge is getting enabled as part of the > pci_enable_device() call of the endpoint? Newer versions of vfio-pci > won't allow binding bridges, it was a bug that it was ever allowed. Our > config space manipulation only knows about normal header types. Actually no, only two PCIe endpoints are assigned to vfio-pci. The endpoints are two different functions on one PCIe device if that matters. > >> 2. What's the recommended way to enable BusMaster with your change >> now? Should my driver map the config space region and set the >> BusMaster bit? Or should I have a separate command to enable the bit >> before opening the device? > > VFIO is designed to be a complete interface to the device, why would you > write a driver that makes use of VFIO that has pre-conditions of > manipulating the device state outside of VFIO? There's no additional > mapping of config space required, you already have access to it through > the device file descriptor. It should simply be a matter of doing a > read-modify-write at the proper offset to toggle the command register. > QEMU uses pread(2) and pwrite(2) for this, but any equivalent tool > should work as well. Thanks, Yes, I'll use pread/pwrite. Thank you! -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
