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Date: Mon, 17 Aug 2020 02:12:44 +0000 From: "Tian, Kevin" <kevin.tian@...el.com> To: Jason Gunthorpe <jgg@...dia.com> CC: Alex Williamson <alex.williamson@...hat.com>, "Jiang, Dave" <dave.jiang@...el.com>, "vkoul@...nel.org" <vkoul@...nel.org>, "Dey, Megha" <megha.dey@...el.com>, "maz@...nel.org" <maz@...nel.org>, "bhelgaas@...gle.com" <bhelgaas@...gle.com>, "rafael@...nel.org" <rafael@...nel.org>, "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>, "tglx@...utronix.de" <tglx@...utronix.de>, "hpa@...or.com" <hpa@...or.com>, "Pan, Jacob jun" <jacob.jun.pan@...el.com>, "Raj, Ashok" <ashok.raj@...el.com>, "Liu, Yi L" <yi.l.liu@...el.com>, "Lu, Baolu" <baolu.lu@...el.com>, "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>, "Luck, Tony" <tony.luck@...el.com>, "Lin, Jing" <jing.lin@...el.com>, "Williams, Dan J" <dan.j.williams@...el.com>, "kwankhede@...dia.com" <kwankhede@...dia.com>, "eric.auger@...hat.com" <eric.auger@...hat.com>, "parav@...lanox.com" <parav@...lanox.com>, "Hansen, Dave" <dave.hansen@...el.com>, "netanelg@...lanox.com" <netanelg@...lanox.com>, "shahafs@...lanox.com" <shahafs@...lanox.com>, "yan.y.zhao@...ux.intel.com" <yan.y.zhao@...ux.intel.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>, "Ortiz, Samuel" <samuel.ortiz@...el.com>, "Hossain, Mona" <mona.hossain@...el.com>, "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org> Subject: RE: [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI support for the idxd driver > From: Jason Gunthorpe > Sent: Friday, August 14, 2020 9:35 PM > > On Mon, Aug 10, 2020 at 07:32:24AM +0000, Tian, Kevin wrote: > > > > I would prefer to see that the existing userspace interface have the > > > extra needed bits for virtualization (eg by having appropriate > > > internal kernel APIs to make this easy) and all the emulation to build > > > the synthetic PCI device be done in userspace. > > > > In the end what decides the direction is the amount of changes that > > we have to put in kernel, not whether we call it 'emulation'. > > No, this is not right. The decision should be based on what will end > up more maintable in the long run. > > Yes it would be more code to dis-aggregate some of the things > currently only bundled as uAPI inside VFIO (eg your vSVA argument > above) but once it is disaggregated the maintability of the whole > solution will be better overall, and more drivers will be able to use > this functionality. > Disaggregation is an orthogonal topic to the main divergence in this thread, which is passthrough vs. userspace DMA. I gave detail explanation about the difference between the two in last reply. the possibility of dis-aggregating something between passthrough frameworks (e.g. VFIO and vDPA) is not the reason for growing every userspace DMA framework to be a passthrough framework. Doing that is instead hurting maintainability in general... Thanks Kevin
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