linux-kernel - Re: refactor the i915 GVT support

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Date:   Tue, 3 Aug 2021 17:43:15 +0800
From:   Zhenyu Wang <zhenyuw@...ux.intel.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>
Subject: Re: refactor the i915 GVT support

On 2021.07.29 09:20:22 +0200, Christoph Hellwig wrote:
> On Wed, Jul 28, 2021 at 02:59:25PM -0300, Jason Gunthorpe wrote:
> > On Wed, Jul 28, 2021 at 01:38:58PM +0000, Wang, Zhi A wrote:
> > 
> > > I guess those APIs you were talking about are KVM-only. For other
> > > hypervisors, e.g. Xen, ARCN cannot use the APIs you mentioned. Not
> > > sure if you have already noticed that VFIO is KVM-only right now.
> > 
> > There is very little hard connection between VFIO and KVM, so no, I
> > don't think that is completely true.
> 
> The only connection is the SET_KVM notifier as far as I can tell.
> Which is used by a total of two drivers, including i915/gvt.  That
> being said gvt does not only use vfio, but also does quite a few
> direct cals to KVM.

yeah, we mostly combined VFIO into hypervisor specific thing before,
e.g interface to set vgpu edid, etc. along with kvm specific calls.

> 
> > In an event, an in-tree version of other hypervisor support for GVT
> > needs to go through enabling VFIO support so that the existing API
> > multiplexers we have can be used properly, not adding a shim layer
> > trying to recreate VFIO inside a GPU driver.
> 
> Yes.  And if we go back to actually looking at the series a lot of
> it just removes entirely pointless indirect calls that go to generic
> code and not even the kvm code, or questionable data structure designs.
> If we were to support another upstream hypervisor we'd just need to
> union a few fields in struct intel_gpu and maybe introduce a few
> methods.  Preferably in a way that avoids expensive indirect calls
> in the fast path.

ok, agree on that.

Acked-by: Zhenyu Wang <zhenyuw@...ux.intel.com>

Thanks a lot for this effort!

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