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From: Alex Williamson <alex.williamson@redhat.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	"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>,
	"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>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"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: Mon, 27 Apr 2020 07:19:39 -0600	[thread overview]
Message-ID: <20200427071939.06aa300e@x1.home> (raw)
In-Reply-To: <20200427115818.GE13640@mellanox.com>

On Mon, 27 Apr 2020 08:58:18 -0300
Jason Gunthorpe <jgg@mellanox.com> wrote:

> On Sun, Apr 26, 2020 at 09:43:55PM -0600, Alex Williamson wrote:
> > On Sun, 26 Apr 2020 16:13:57 -0300
> > Jason Gunthorpe <jgg@mellanox.com> wrote:
> >   
> > > On Sun, Apr 26, 2020 at 05:18:59AM +0000, Tian, Kevin wrote:
> > >   
> > > > > > 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.    
> > > 
> > > There have been several abusive proposals of vfio-mdev, everything
> > > from a way to create device drivers to this kind of generic emulation
> > > framework.
> > >   
> > > > 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...    
> > > 
> > > It is appropriate when non-PCI standard techniques are needed to do
> > > raw device assignment, just like VFIO.
> > > 
> > > Basically if vfio-pci is already doing it then it seems reasonable
> > > that vfio-mdev should do the same. This mission creep where vfio-mdev
> > > gains functionality far beyond VFIO is the problem.  
> > 
> > Ehm, vfio-pci emulates BARs too.  We also emulate FLR, power
> > management, DisINTx, and VPD.  FLR, PM, and VPD all have device
> > specific quirks in the host kernel, and I've generally taken the stance
> > that would should take advantage of those quirks, not duplicate them in
> > userspace and not invent new access mechanisms/ioctls for each of them.
> > Emulating DisINTx is convenient since we must have a mechanism to mask
> > INTx, whether it's at the device or the APIC, so we can pretend the
> > hardware supports it.  BAR emulation is really too trivial to argue
> > about, the BARs mean nothing to the physical device mapping, they're
> > simply scratch registers that we mask out the alignment bits on read.
> > vfio-pci is a mix of things that we decide are too complicated or
> > irrelevant to emulate in the kernel and things that take advantage of
> > shared quirks or are just too darn easy to worry about.  BARs fall into
> > that latter category, any sort of mapping into VM address spaces is
> > necessarily done in userspace, but scratch registers that are masked on
> > read, *shrug*, vfio-pci does that.  Thanks,  
> 
> It is not trivial masking. It is a 2000 line patch doing comprehensive
> emulation.

Not sure what you're referring to, I see about 30 lines of code in
vdcm_vidxd_cfg_write() that specifically handle writes to the 4 BARs in
config space and maybe a couple hundred lines of code in total handling
config space emulation.  Thanks,

Alex


  reply	other threads:[~2020-04-27 13:19 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
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 [this message]
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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