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From: Jason Gunthorpe <jgg@mellanox.com>
To: "Raj, Ashok" <ashok.raj@intel.com>
Cc: "Tian, Kevin" <kevin.tian@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>,
	"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: Thu, 23 Apr 2020 16:12:17 -0300	[thread overview]
Message-ID: <20200423191217.GD13640@mellanox.com> (raw)
In-Reply-To: <20200422211436.GA103345@otc-nc-03>

On Wed, Apr 22, 2020 at 02:14:36PM -0700, Raj, Ashok wrote:
> Hi Jason
> 
> > > > 
> > > > I'm feeling really skeptical that adding all this PCI config space and
> > > > MMIO BAR emulation to the kernel just to cram this into a VFIO
> > > > interface is a good idea, that kind of stuff is much safer in
> > > > userspace.
> > > > 
> > > > Particularly since vfio is not really needed once a driver is using
> > > > the PASID stuff. We already have general code for drivers to use to
> > > > attach a PASID to a mm_struct - and using vfio while disabling all the
> > > > DMA/iommu config really seems like an abuse.
> > > 
> > > Well, this series is for virtualizing idxd device to VMs, instead of
> > > supporting SVA for bare metal processes. idxd implements a
> > > hardware-assisted mediated device technique called Intel Scalable
> > > I/O Virtualization,
> > 
> > I'm familiar with the intel naming scheme.
> > 
> > > which allows each Assignable Device Interface (ADI, e.g. a work
> > > queue) tagged with an unique PASID to ensure fine-grained DMA
> > > isolation when those ADIs are assigned to different VMs. For this
> > > purpose idxd utilizes the VFIO mdev framework and IOMMU aux-domain
> > > extension. Bare metal SVA will be enabled for idxd later by using
> > > the general SVA code that you mentioned.  Both paths will co-exist
> > > in the end so there is no such case of disabling DMA/iommu config.
> >  
> > Again, if you will have a normal SVA interface, there is no need for a
> > VFIO version, just use normal SVA for both.
> > 
> > PCI emulation should try to be in userspace, not the kernel, for
> > security.
> 
> Not sure we completely understand your proposal. Mediated devices
> are software constructed and they have protected resources like
> interrupts and stuff and VFIO already provids abstractions to export
> to user space.
> 
> Native SVA is simply passing the process CR3 handle to IOMMU so
> IOMMU knows how to walk process page tables, kernel handles things
> like page-faults, doing device tlb invalidations and such.

> That by itself doesn't translate to what a guest typically does
> with a VDEV. There are other control paths that need to be serviced
> from the kernel code via VFIO. For speed path operations like
> ringing doorbells and such they are directly managed from guest.

You don't need vfio to mmap BAR pages to userspace. The unique thing
that vfio gives is it provides a way to program the classic non-PASID
iommu, which you are not using here.

> How do you propose to use the existing SVA api's  to also provide
> full device emulation as opposed to using an existing infrastructure 
> that's already in place?

You'd provide the 'full device emulation' in userspace (eg qemu),
along side all the other device emulation. Device emulation does not
belong in the kernel without a very good reason.

You get the doorbell BAR page from your own char dev

You setup a PASID IOMMU configuration over your own char dev

Interrupt delivery is triggering a generic event fd

What is VFIO needed for?
 
> Perhaps Alex can ease Jason's concerns?

Last we talked Alex also had doubts on what mdev should be used
for. It is a feature that seems to lack boundaries, and I'll note that
when the discussion came up for VDPA, they eventually choose not to
use VFIO.

Jason

  reply	other threads:[~2020-04-23 19:12 UTC|newest]

Thread overview: 89+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21 23:33 [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver 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 [this message]
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
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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