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From: "Dey, Megha" <megha.dey@intel.com>
To: Jason Gunthorpe <jgg@mellanox.com>, Marc Zyngier <maz@kernel.org>
Cc: "Jiang, Dave" <dave.jiang@intel.com>,
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Subject: RE: [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI irq domain
Date: Wed, 5 Aug 2020 19:18:39 +0000
Message-ID: <96a1eb5ccc724790b5404a642583919d@intel.com> (raw)
In-Reply-To: <20200722195928.GN2021248@mellanox.com>

Hi Jason,

> -----Original Message-----
> From: Jason Gunthorpe <jgg@mellanox.com>
> Sent: Wednesday, July 22, 2020 12:59 PM
> To: Marc Zyngier <maz@kernel.org>
> Cc: Jiang, Dave <dave.jiang@intel.com>; vkoul@kernel.org; Dey, Megha
> <megha.dey@intel.com>; bhelgaas@google.com; rafael@kernel.org;
> gregkh@linuxfoundation.org; tglx@linutronix.de; hpa@zytor.com;
> alex.williamson@redhat.com; Pan, Jacob jun <jacob.jun.pan@intel.com>; Raj,
> Ashok <ashok.raj@intel.com>; Liu, Yi L <yi.l.liu@intel.com>; Lu, Baolu
> <baolu.lu@intel.com>; Tian, Kevin <kevin.tian@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; eric.auger@redhat.com; parav@mellanox.com;
> Hansen, Dave <dave.hansen@intel.com>; netanelg@mellanox.com;
> shahafs@mellanox.com; yan.y.zhao@linux.intel.com; pbonzini@redhat.com;
> Ortiz, Samuel <samuel.ortiz@intel.com>; Hossain, Mona
> <mona.hossain@intel.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 v2 02/18] irq/dev-msi: Add support for a new DEV_MSI
> irq domain
> 
> On Wed, Jul 22, 2020 at 07:52:33PM +0100, Marc Zyngier wrote:
> 
> > Which is exactly what platform-MSI already does. Why do we need
> > something else?
> 
> It looks to me like all the code is around managing the
> dev->msi_domain of the devices.
> 
> The intended use would have PCI drivers create children devices using mdev or
> virtbus and those devices wouldn't have a msi_domain from the platform. Looks
> like platform_msi_alloc_priv_data() fails immediately because dev->msi_domain
> will be NULL for these kinds of devices.
> 
> Maybe that issue should be handled directly instead of wrappering
> platform_msi_*?
> 
> For instance a trivial addition to the platform_msi API:
> 
>   platform_msi_assign_domain(struct_device *newly_created_virtual_device,
>                              struct device *physical_device);
> 
> Which could set the msi_domain of new device using the topology of
> physical_device to deduce the correct domain?
> 
> Then the question is how to properly create a domain within the hardware
> topology of physical_device with the correct parameters for the platform.
> 
> Why do we need a dummy msi_domain anyhow? Can this just use
> physical_device->msi_domain directly? (I'm at my limit here of how much of this
> I remember, sorry)
> 
> If you solve that it should solve the remapping problem too, as the
> physical_device is already assigned by the platform to a remapping irq domain if
> that is what the platform wants.

Yeah most of what you said is right. For the most part, we are simply introducing a new IRQ domain
which provides specific domain info ops for the classes of devices which want to provide custom
mask/unmask callbacks..

Also, from your other comments, I've realized the same IRQ domain can be used when interrupt
remapping is enabled/disabled.

Hence we will only have one create_dev_msi_domain which can be called by any device driver that
wants to use the dev-msi IRQ domain to alloc/free IRQs. It would be the responsibility of the device
driver to provide the correct device and update the dev->msi_domain.
  
> 
> >> +	parent = irq_get_default_host();
> > Really? How is it going to work once you have devices sending their
> > MSIs to two different downstream blocks? This looks rather
> > short-sighted.
> 
> .. and fix this too, the parent domain should be derived from the topology of the
> physical_device which is originating the interrupt messages.
> 
Yes

> > On the other hand, masking an interrupt is an irqchip operation, and
> > only concerns the irqchip level. Here, you seem to be making it an
> > end-point operation, which doesn't really make sense to me. Or is this
> > device its own interrupt controller as well? That would be extremely
> > surprising, and I'd expect some block downstream of the device to be
> > able to control the masking of the interrupt.
> 
> These are message interrupts so they originate directly from the device and
> generally travel directly to the CPU APIC. On the wire there is no difference
> between a MSI, MSI-X and a device using the dev-msi approach.
> 
> IIRC on Intel/AMD at least once a MSI is launched it is not maskable.
> 
> So the model for MSI is always "mask at source". The closest mapping to the
> Linux IRQ model is to say the end device has a irqchip that encapsulates the
> ability of the device to generate the MSI in the first place.
> 
> It looks like existing platform_msi drivers deal with "masking"
> implicitly by halting the device interrupt generation before releasing the
> interrupt and have no way for the generic irqchip layer to mask the interrupt.
> 
> I suppose the motivation to make it explicit is related to vfio using the generic
> mask/unmask functionality?
> 
> Explicit seems better, IMHO.

I don't think I understand this fully, ive still kept the device specific mask/unmask calls in the next
patch series, please let me know if it needs further modifications.
> 
> Jason

  parent reply index

Thread overview: 97+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-21 16:02 [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI support for the idxd driver Dave Jiang
2020-07-21 16:02 ` [PATCH RFC v2 01/18] platform-msi: Introduce platform_msi_ops Dave Jiang
2020-07-21 16:02 ` [PATCH RFC v2 02/18] irq/dev-msi: Add support for a new DEV_MSI irq domain Dave Jiang
2020-07-21 16:13   ` Jason Gunthorpe
2020-07-22 16:50     ` Dey, Megha
2020-07-22 18:52   ` Marc Zyngier
2020-07-22 19:59     ` Jason Gunthorpe
2020-07-23  8:51       ` Marc Zyngier
2020-07-24  0:16         ` Jason Gunthorpe
2020-07-24  0:36           ` Thomas Gleixner
2020-08-05 19:18       ` Dey, Megha [this message]
2020-08-05 22:15         ` Jason Gunthorpe
2020-08-05 22:36           ` Dey, Megha
2020-08-05 22:53             ` Jason Gunthorpe
2020-08-06  0:13               ` Dey, Megha
2020-08-06  0:19                 ` Jason Gunthorpe
2020-08-06  0:32                   ` Dey, Megha
2020-08-06  0:46                     ` Jason Gunthorpe
2020-08-06 17:10                     ` Thomas Gleixner
2020-08-06 17:58                       ` Dey, Megha
2020-08-06 20:21                         ` Thomas Gleixner
2020-08-06 22:27                           ` Dey, Megha
2020-08-07  8:48                             ` Thomas Gleixner
2020-08-07 12:06                           ` Jason Gunthorpe
2020-08-07 12:38                             ` gregkh
2020-08-07 13:34                               ` Jason Gunthorpe
2020-08-07 16:47                                 ` Thomas Gleixner
2020-08-07 17:54                                   ` Dey, Megha
2020-08-07 18:39                                     ` Jason Gunthorpe
2020-08-07 20:31                                       ` Dey, Megha
2020-08-08 19:47                                     ` Thomas Gleixner
2020-08-10 21:46                                       ` Thomas Gleixner
2020-08-11  9:53                                         ` Thomas Gleixner
2020-08-11 18:46                                           ` Dey, Megha
2020-08-11 21:25                                             ` Thomas Gleixner
2020-08-11 18:39                                       ` Dey, Megha
2020-08-11 22:39                                         ` Thomas Gleixner
2020-08-07 15:22                             ` Thomas Gleixner
2020-08-05 18:55     ` Dey, Megha
2020-07-21 16:02 ` [PATCH RFC v2 03/18] irq/dev-msi: Create IR-DEV-MSI " Dave Jiang
2020-07-21 16:21   ` Jason Gunthorpe
2020-07-22 17:03     ` Dey, Megha
2020-07-22 17:33       ` Jason Gunthorpe
2020-07-22 20:44   ` Thomas Gleixner
2020-08-05 19:02     ` Dey, Megha
2020-07-21 16:02 ` [PATCH RFC v2 04/18] irq/dev-msi: Introduce APIs to allocate/free dev-msi interrupts Dave Jiang
2020-07-21 16:25   ` Jason Gunthorpe
2020-07-22 17:05     ` Dey, Megha
2020-07-22 17:35       ` Jason Gunthorpe
2020-08-05 20:19         ` Dey, Megha
2020-07-21 16:02 ` [PATCH RFC v2 05/18] dmaengine: idxd: add support for readonly config devices Dave Jiang
2020-07-21 16:02 ` [PATCH RFC v2 06/18] dmaengine: idxd: add interrupt handle request support Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 07/18] dmaengine: idxd: add DEV-MSI support in base driver Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 08/18] dmaengine: idxd: add device support functions in prep for mdev Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 09/18] dmaengine: idxd: add basic mdev registration and helper functions Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 10/18] dmaengine: idxd: add emulation rw routines Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 11/18] dmaengine: idxd: prep for virtual device commands Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 12/18] dmaengine: idxd: virtual device commands emulation Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 13/18] dmaengine: idxd: ims setup for the vdcm Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 14/18] dmaengine: idxd: add mdev type as a new wq type Dave Jiang
2020-07-21 16:03 ` [PATCH RFC v2 15/18] dmaengine: idxd: add dedicated wq mdev type Dave Jiang
2020-07-21 16:04 ` [PATCH RFC v2 16/18] dmaengine: idxd: add new wq state for mdev Dave Jiang
2020-07-21 16:04 ` [PATCH RFC v2 17/18] dmaengine: idxd: add error notification from host driver to mediated device Dave Jiang
2020-07-21 16:04 ` [PATCH RFC v2 18/18] dmaengine: idxd: add ABI documentation for mediated device support Dave Jiang
2020-07-21 16:28 ` [PATCH RFC v2 00/18] Add VFIO mediated device support and DEV-MSI support for the idxd driver Greg KH
2020-07-21 17:17   ` Dave Jiang
2020-07-21 21:35   ` Dan Williams
2020-07-21 16:45 ` Jason Gunthorpe
2020-07-21 18:00   ` Dave Jiang
2020-07-22 17:31     ` Dey, Megha
2020-07-22 18:16       ` Jason Gunthorpe
2020-07-21 23:54   ` Tian, Kevin
2020-07-24  0:19     ` Jason Gunthorpe
2020-08-06  1:22       ` Alex Williamson
2020-08-07 12:19         ` Jason Gunthorpe
2020-08-10  7:32           ` Tian, Kevin
2020-08-11 17:00             ` Alex Williamson
2020-08-12  1:58               ` Tian, Kevin
2020-08-12  2:36                 ` Alex Williamson
2020-08-12  3:35                   ` Tian, Kevin
2020-08-12  3:28             ` Jason Wang
2020-08-12  4:05               ` Tian, Kevin
2020-08-13  4:33                 ` Jason Wang
2020-08-13  5:26                   ` Tian, Kevin
2020-08-13  6:01                     ` Jason Wang
2020-08-14 13:23                       ` Jason Gunthorpe
2020-08-17  2:24                         ` Tian, Kevin
2020-08-14 13:35             ` Jason Gunthorpe
2020-08-17  2:12               ` Tian, Kevin
2020-08-18  0:43                 ` Jason Gunthorpe
2020-08-18  1:09                   ` Tian, Kevin
2020-08-18 11:50                     ` Jason Gunthorpe
2020-08-18 16:27                       ` Paolo Bonzini
2020-08-18 16:49                         ` Jason Gunthorpe
2020-08-18 17:05                           ` Paolo Bonzini
2020-08-18 17:18                             ` Jason Gunthorpe
2020-08-19  7:29                       ` Tian, Kevin

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