On 16/10/17 17:00, David Gibson wrote: > On Mon, Oct 16, 2017 at 04:54:08PM +1100, Alexey Kardashevskiy wrote: >> On 12/10/17 02:35, Benjamin Herrenschmidt wrote: >>> On Wed, 2017-10-11 at 13:56 +1100, Alexey Kardashevskiy wrote: >>>> Oopsie. This is because I overlooked it. Others do not use it. So I do need >>>> a file. But in the current scheme where all BARs share one fd - it won't >>>> work - I simply cannot allow WC on non-prefetchable BARs :-/ >>> >>> This is an oversight in the design of VFIO-PCI, it should have a way to >>> specify write combine, either implicitely via such an arch hook, or >>> explicitely via an ioctl prior to mapping the BARs for example. >>> >>> Alex, what do you reckon is the best approach here ? >> >> /me wonders if it is yet another issue for the dead issues bucket, just >> like the msix mapping one :) > > Maybe. Alexey, maybe you can make up a list of things that we (me, > you, BenH) need to discuss with Alex W at KVM Forum? "you" - you meant me? I am not coming over there :( The list is: 1. Allow msix mapping to the userspace (to address non-64k-aligned msix bar) 2. Allow write combining in vfio for the userspace (kvm guest is kinda special and may simply ignore mapping flags in some configs but PPC radix guests still rely on this) 3. what callback and where needs to be added to inform HV/PR KVM about VFIO group, like IOMMUMR::add_vfio_group() proposal or something. Thanks! -- Alexey
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