On Fri, Dec 15, 2017 at 09:04:28AM -0700, Alex Williamson wrote: > On Fri, 15 Dec 2017 15:07:31 +1100 > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > On Tue, Dec 12, 2017 at 04:21:31PM +1100, Alexey Kardashevskiy wrote: > > > This makes use of a new VFIO_REGION_INFO_CAP_MSIX_MAPPABLE capability > > > which tells that a region with MSIX data can be mapped entirely, i.e. > > > the VFIO PCI driver won't prevent MSIX vectors area from being mapped. > > > > > > This adds a "msix-no-mmap" property to the vfio-pci device, it is "true" > > > by default and "false" for pseries-2.12+ machines. > > > > > > This requites kernel's "vfio-pci: Allow mapping MSIX BAR" > > > https://www.spinics.net/lists/kvm/msg160282.html > > > > > > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > > > --- > > > > > > This is an RFC as it requires kernel headers update which is not there > > > yet. > > > > > > I'd like to make it "msix-mmap" (without "no") but could not find a way > > > of enabling a device property for machine versions newer than some value. > > > > > > I changed 2.11 machine just for the demonstration purpose. > > > > As Alex says, the mmap()ability of the MSI-X BAR isn't really the > > point. The point is whether we need to intercept guest MMIOs to the > > MSI-X region. Still, the logic's basically right, just rename your > > property to, say, "intercept_msix_mmio". It would be true by default, > > set to false by the pseries machine type. > > > > I don't think you actually need to make it vary depending on the > > version of the pseries machine type: whether the BAR is mmap()ed or > > qemu emulated shouldn't be a guest visible change. No PAPR guest > > should have been directly poking the MSI-X region (ever), so we > > shouldn't need to intercept the region even for old versions. > > I have to ask, is the vfio-pci driver really the right point in the VM > to be understanding whether the platform requires MSI-X MMIO > emulation? vfio-pci is only unique here in that enabling that > emulation harms performance, but AIUI it's unused on any device and > there may eventually be other devices affected in the same way as > vfio-pci. So should there be some post-realize platform code that > disables MSI-X MemoryRegions or should the MSI-X code call out to some > platform hook to determine whether to enable emulation? Seems like a > case where the impact might be unique to vfio, but the root of the > problem is not. Thanks,
That's a good point. If we can reasonably do it at the level of a
generic PCI device, that would be preferable.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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