Re: refactor the i915 GVT support

From: Zhenyu Wang <zhenyuw@linux.intel.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	"intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	Zhenyu Wang <zhenyuw@linux.intel.com>,
	Gerd Hoffmann <kraxel@redhat.com>,
	"Vivi, Rodrigo" <rodrigo.vivi@intel.com>,
	"intel-gvt-dev@lists.freedesktop.org"
	<intel-gvt-dev@lists.freedesktop.org>,
	"Wang, Zhi A" <zhi.a.wang@intel.com>
Subject: Re: refactor the i915 GVT support
Date: Tue, 3 Aug 2021 17:43:15 +0800	[thread overview]
Message-ID: <20210803094315.GF13928@zhen-hp.sh.intel.com> (raw)
In-Reply-To: <20210729072022.GB31896@lst.de>

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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@linux.intel.com>

Thanks a lot for this effort!

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