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. Bjorn > --- > > Alex Williamson (3): > PCI: Extend and export pci_msi_supported() for multivector MSI > PCI/x86: Add arch_supports_multivector_msi() hook > PCI/MSI: Initial hook for archs to declare multivector MSI support > > > arch/x86/include/asm/x86_init.h | 1 + > arch/x86/kernel/x86_init.c | 6 ++++++ > drivers/iommu/irq_remapping.c | 6 ++++++ > drivers/pci/msi.c | 20 +++++++++++++++++--- > include/linux/msi.h | 1 + > include/linux/pci.h | 3 +++ > 6 files changed, 34 insertions(+), 3 deletions(-) -- 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
