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From: "Dey, Megha" <megha.dey@linux.intel.com>
To: Jason Gunthorpe <jgg@mellanox.com>, Dave Jiang <dave.jiang@intel.com>
Cc: vkoul@kernel.org, maz@kernel.org, bhelgaas@google.com,
	rafael@kernel.org, gregkh@linuxfoundation.org,
	tglx@linutronix.de, hpa@zytor.com, alex.williamson@redhat.com,
	jacob.jun.pan@intel.com, ashok.raj@intel.com, yi.l.liu@intel.com,
	baolu.lu@intel.com, kevin.tian@intel.com,
	sanjay.k.kumar@intel.com, tony.luck@intel.com,
	jing.lin@intel.com, dan.j.williams@intel.com,
	kwankhede@nvidia.com, eric.auger@redhat.com, parav@mellanox.com,
	dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, linux-pci@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: Wed, 22 Apr 2020 16:04:20 -0700	[thread overview]
Message-ID: <d6b3c133-ac19-21af-b7a7-b9e7166b8166@linux.intel.com> (raw)
In-Reply-To: <20200421235442.GO11945@mellanox.com>



On 4/21/2020 4:54 PM, Jason Gunthorpe wrote:
> On Tue, Apr 21, 2020 at 04:33:46PM -0700, Dave Jiang wrote:
>> The actual code is independent of the stage 2 driver code submission that adds
>> support for SVM, ENQCMD(S), PASID, and shared workqueues. This code series will
>> support dedicated workqueue on a guest with no vIOMMU.
>>    
>> A new device type "mdev" is introduced for the idxd driver. This allows the wq
>> to be dedicated to the usage of a VFIO mediated device (mdev). Once the work
>> queue (wq) is enabled, an uuid generated by the user can be added to the wq
>> through the uuid sysfs attribute for the wq.  After the association, a mdev can
>> be created using this UUID. The mdev driver code will associate the uuid and
>> setup the mdev on the driver side. When the create operation is successful, the
>> uuid can be passed to qemu. When the guest boots up, it should discover a DSA
>> device when doing PCI discovery.
> 
> 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.
> 
> A /dev/idxd char dev that mmaps a bar page and links it to a PASID
> seems a lot simpler and saner kernel wise.
> 
>> The mdev utilizes Interrupt Message Store or IMS[3] instead of MSIX for
>> interrupts for the guest. This preserves MSIX for host usages and also allows a
>> significantly larger number of interrupt vectors for guest usage.
> 
> I never did get a reply to my earlier remarks on the IMS patches.
> 
> The concept of a device specific addr/data table format for MSI is not
> Intel specific. This should be general code. We have a device that can
> use this kind of kernel capability today.
> 

<resending to the mailing list, I had incorrect email options set>

Hi Jason,

I am sorry if I did not address your comments earlier.

The present IMS code is quite generic, most of the code is in the 
drivers/ folder. We basically introduce 2 APIS: allocate and free IMS 
interrupts and a IMS IRQ domain to allocate these interrupts from. These 
APIs are architecture agnostic.

We also introduce a new IMS IRQ domain which is architecture specific. 
This is because IMS generates interrupts only in the remappable format, 
hence interrupt remapping should be enabled for IMS. Currently, the 
interrupt remapping code is only available for Intel and AMD and I don’t 
see anything for ARM.

If a new architecture would want to use IMS, they must simply introduce 
a new IMS IRQ domain. I am not sure if there is any other way around 
this. If you have any ideas, please let me know.

Also, could you give more details on the device that could use IMS? Do 
you have some driver code already? We could then see if and how the 
current IMS code could be made more generic.

> Jason
> 

  parent reply	other threads:[~2020-04-22 23:04 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
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 [this message]
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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