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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: "Raj, Ashok" <ashok.raj@intel.com>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"vkoul@kernel.org" <vkoul@kernel.org>,
	"megha.dey@linux.intel.com" <megha.dey@linux.intel.com>,
	"maz@kernel.org" <maz@kernel.org>,
	"bhelgaas@google.com" <bhelgaas@google.com>,
	"rafael@kernel.org" <rafael@kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"Pan, Jacob jun" <jacob.jun.pan@intel.com>,
	"Liu, Yi L" <yi.l.liu@intel.com>,
	"Lu, Baolu" <baolu.lu@intel.com>,
	"Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
	"Luck, Tony" <tony.luck@intel.com>,
	"Lin, Jing" <jing.lin@intel.com>,
	"Williams, Dan J" <dan.j.williams@intel.com>,
	"kwankhede@nvidia.com" <kwankhede@nvidia.com>,
	"eric.auger@redhat.com" <eric.auger@redhat.com>,
	"parav@mellanox.com" <parav@mellanox.com>,
	"dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
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	"x86@kernel.org" <x86@kernel.org>,
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	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: RE: [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver.
Date: Sun, 26 Apr 2020 05:18:59 +0000	[thread overview]
Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D19D8C5486@SHSMSX104.ccr.corp.intel.com> (raw)
In-Reply-To: <20200424181203.GU13640@mellanox.com>

> From: Jason Gunthorpe <jgg@mellanox.com>
> Sent: Saturday, April 25, 2020 2:12 AM
> 
> > > > idxd is just the first device that supports Scalable IOV. We have a
> > > > lot more coming later, in different types. Then putting such
> > > > emulation in user space means that Qemu needs to support all those
> > > > vendor specific interfaces for every new device which supports
> > >
> > > It would be very sad to see an endless amount of device emulation code
> > > crammed into the kernel. Userspace is where device emulation is
> > > supposed to live. For security
> >
> > I think providing an unified abstraction to userspace is also important,
> > which is what VFIO provides today. The merit of using one set of VFIO
> > API to manage all kinds of mediated devices and VF devices is a major
> > gain. Instead, inventing a new vDPA-like interface for every Scalable-IOV
> > or equivalent device is just overkill and doesn't scale. Also the actual
> > emulation code in idxd driver is actually small, if putting aside the PCI
> > config space part for which I already explained most logic could be shared
> > between mdev device drivers.
> 
> If it was just config space you might have an argument, VFIO already
> does some config space mangling, but emulating BAR space is out of
> scope of VFIO, IMHO.

out of scope of vfio-pci, but in scope of vfio-mdev. btw I feel that most
of your objections are actually related to the general idea of vfio-mdev.
Scalable IOV just uses PASID to harden DMA isolation in mediated
pass-through usage which vfio-mdev enables. Then are you just opposing
the whole vfio-mdev? If not, I'm curious about the criteria in your mind 
about when using vfio-mdev is good...

> 
> I also think it is disingenuous to pretend this is similar to
> SR-IOV. SR-IOV is self contained and the BAR does not require
> emulation. What you have here sounds like it is just an ordinary

technically Scalable IOV is definitely different from SR-IOV. It's 
simpler in hardware. And we're not emulating SR-IOV. The point
is just in usage-wise we want to present a consistent user 
experience just like passing through a PCI endpoint (PF or VF) device
through vfio eco-system, including various userspace VMMs (Qemu,
firecracker, rust-vmm, etc.), middleware (Libvirt), and higher level 
management stacks. 

> multi-queue device with the ability to PASID tag queues for IOMMU
> handling. This is absolutely not SRIOV - it is much closer to VDPA,
> which isn't using mdev.
> 
> Further, I disagree with your assessment that this doesn't scale. You
> already said you plan a normal user interface for idxd, so instead of
> having a single sane user interface (ala VDPA) idxd now needs *two*. If
> this is the general pattern of things to come, it is a bad path.
> 
> The only thing we get out of this is someone doesn't have to write a
> idxd emulation driver in qemu, instead they have to write it in the
> kernel. I don't see how that is a win for the ecosystem.
> 

No. The clear win is on leveraging classic VFIO iommu and its eco-system
as explained above.

Thanks
Kevin

  reply	other threads:[~2020-04-26  5:19 UTC|newest]

Thread overview: 89+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21 23:33 Dave Jiang
2020-04-21 23:33 ` [PATCH RFC 01/15] drivers/base: Introduce platform_msi_ops Dave Jiang
2020-04-26  7:01   ` Greg KH
2020-04-27 21:38     ` Dave Jiang
2020-04-28  7:34       ` Greg KH
2020-04-21 23:33 ` [PATCH RFC 02/15] drivers/base: Introduce a new platform-msi list Dave Jiang
2020-04-25 21:13   ` Thomas Gleixner
2020-05-04  0:08     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 03/15] drivers/base: Allocate/free platform-msi interrupts by group Dave Jiang
2020-04-25 21:23   ` Thomas Gleixner
2020-05-04  0:08     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 04/15] drivers/base: Add support for a new IMS irq domain Dave Jiang
2020-04-23 20:11   ` Jason Gunthorpe
2020-05-01 22:30     ` Dey, Megha
2020-05-03 22:25       ` Jason Gunthorpe
2020-05-03 22:40         ` Dey, Megha
2020-05-03 22:46           ` Jason Gunthorpe
2020-05-04  0:25             ` Dey, Megha
2020-05-04 12:14               ` Jason Gunthorpe
2020-05-06 10:27                 ` Tian, Kevin
2020-04-25 21:38   ` Thomas Gleixner
2020-05-04  0:11     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 05/15] ims-msi: Add mask/unmask routines Dave Jiang
2020-04-25 21:49   ` Thomas Gleixner
2020-05-04  0:16     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 06/15] ims-msi: Enable IMS interrupts Dave Jiang
2020-04-25 22:13   ` Thomas Gleixner
2020-05-04  0:17     ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 07/15] Documentation: Interrupt Message store Dave Jiang
2020-04-23 20:04   ` Jason Gunthorpe
2020-05-01 22:32     ` Dey, Megha
2020-05-03 22:28       ` Jason Gunthorpe
2020-05-03 22:41         ` Dey, Megha
2020-04-21 23:34 ` [PATCH RFC 08/15] vfio/mdev: Add a member for iommu domain in mdev_device Dave Jiang
2020-04-21 23:34 ` [PATCH RFC 09/15] vfio/type1: Save domain when attach domain to mdev Dave Jiang
2020-04-21 23:34 ` [PATCH RFC 10/15] dmaengine: idxd: add config support for readonly devices Dave Jiang
2020-04-21 23:34 ` [PATCH RFC 11/15] dmaengine: idxd: add IMS support in base driver Dave Jiang
2020-04-21 23:35 ` [PATCH RFC 12/15] dmaengine: idxd: add device support functions in prep for mdev Dave Jiang
2020-04-21 23:35 ` [PATCH RFC 13/15] dmaengine: idxd: add support for VFIO mediated device Dave Jiang
2020-04-21 23:35 ` [PATCH RFC 14/15] dmaengine: idxd: add error notification from host driver to " Dave Jiang
2020-04-21 23:35 ` [PATCH RFC 15/15] dmaengine: idxd: add ABI documentation for mediated device support Dave Jiang
2020-04-21 23:54 ` [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver Jason Gunthorpe
2020-04-22  0:53   ` Tian, Kevin
2020-04-22 11:50     ` Jason Gunthorpe
2020-04-22 21:14       ` Raj, Ashok
2020-04-23 19:12         ` Jason Gunthorpe
2020-04-24  3:27           ` Tian, Kevin
2020-04-24 12:44             ` Jason Gunthorpe
2020-04-24 16:25               ` Tian, Kevin
2020-04-24 18:12                 ` Jason Gunthorpe
2020-04-26  5:18                   ` Tian, Kevin [this message]
2020-04-26 19:13                     ` Jason Gunthorpe
2020-04-27  3:43                       ` Alex Williamson
2020-04-27 11:58                         ` Jason Gunthorpe
2020-04-27 13:19                           ` Alex Williamson
2020-04-27 13:22                             ` Jason Gunthorpe
2020-04-27 14:18                               ` Alex Williamson
2020-04-27 14:25                                 ` Jason Gunthorpe
2020-04-27 15:41                                   ` Alex Williamson
2020-04-27 16:16                                     ` Jason Gunthorpe
2020-04-27 16:25                                       ` Dave Jiang
2020-04-27 21:56                                         ` Jason Gunthorpe
2020-04-29  9:42                               ` Tian, Kevin
2020-05-08 20:47                                 ` Raj, Ashok
2020-05-08 23:16                                   ` Jason Gunthorpe
2020-05-08 23:52                                     ` Dave Jiang
2020-05-09  0:09                                     ` Raj, Ashok
2020-05-09 12:21                                       ` Jason Gunthorpe
2020-05-13  2:29                                         ` Jason Wang
2020-05-13  8:30                                         ` Tian, Kevin
2020-05-13 12:40                                           ` Jason Gunthorpe
2020-04-27 12:13                       ` Tian, Kevin
2020-04-27 12:55                         ` Jason Gunthorpe
2020-04-22 21:24   ` Dan Williams
2020-04-23 19:17     ` Dan Williams
2020-04-23 19:49       ` Jason Gunthorpe
2020-05-01 22:31         ` Dey, Megha
2020-05-03 22:21           ` Jason Gunthorpe
2020-05-03 22:32             ` Dey, Megha
2020-04-23 19:18     ` Jason Gunthorpe
2020-05-01 22:31       ` Dey, Megha
2020-05-03 22:22         ` Jason Gunthorpe
2020-05-03 22:31           ` Dey, Megha
2020-05-03 22:36             ` Jason Gunthorpe
2020-05-04  0:20               ` Dey, Megha
2020-04-22 23:04   ` Dey, Megha
2020-04-23 19:44     ` Jason Gunthorpe
2020-05-01 22:32       ` Dey, Megha
2020-04-24  6:31   ` Jason Wang

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