On Thu, 2015-01-08 at 09:15 -0700, Bjorn Helgaas wrote: > On Fri, Nov 21, 2014 at 03:08:27PM -0700, Alex Williamson wrote: > > I'd like to make vfio-pci capable of manipulating the device exposed > > to the user such that if the host can only support a single MSI > > vector then we hide the fact that the device itself may actually be > > able to support more. When we virtualize PCI config space and > > interrupt setup there's no PCI protocol for the device failing to > > allocate the number of vectors that it said were available. If the > > userspace driver is a guest operating system, it certainly doesn't > > expect this to fail. I don't think we can ever guarantee that a > > multi-vector request will succeed, but we can certainly guarantee > > that it will fail if the platform doesn't support it. > > > > An example device is the Atheros AR93xxx running in a Windows 7 VM. > > Both the device and the guest OS support multiple MSI vectors. With > > interrupt remapping, such that the host supports multivector, the > > device works well in the guest. With interrupt remapping disabled, > > the device is far less reliable because of the mismatch in MSI > > programming vs driver configuration and often fails. If vfio-pci > > can test whether multiple vectors are supported, then we can make it > > work reliably in both cases by adjusting the exposed MSI capability, > > like in this patch that would follow this series: > > > > https://github.com/awilliam/linux-vfio/commit/9ace67515680 > > > > With this series, only x86 w/ interrupt remapping will advertise > > support for multiple MSI vectors. In surveying the code, I couldn't > > find any other archs that allowed it, but I'll take corrections if > > that's untrue. Thanks, > > Per Thomas' comments and your possible workaround if we don't have > pci_msi_supported(), I'm going to ignore these for now. Let me know if > you disagree. Yep, that's fine. I'll either forget about this for a while or kludge something in vfio to know that only x86 with interrupt remapping, which I can test from the IOMMU API, has multivector MSI support. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
