Re: [RFC PATCH kernel] vfio-pci: Allow write combining

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 1830 bytes --]

On Mon, Oct 16, 2017 at 06:36:29PM +1100, Alexey Kardashevskiy wrote:
> 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 :(

Oh.. I thought you were.

> 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.

-- 
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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]