linux-kernel - RE: [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver.

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Date:   Wed, 29 Apr 2020 09:42:20 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...lanox.com>,
        Alex Williamson <alex.williamson@...hat.com>
CC:     "Raj, Ashok" <ashok.raj@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "megha.dey@...ux.intel.com" <megha.dey@...ux.intel.com>,
        "maz@...nel.org" <maz@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "hpa@...or.com" <hpa@...or.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Lu, Baolu" <baolu.lu@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Lin, Jing" <jing.lin@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [PATCH RFC 00/15] Add VFIO mediated device support and IMS
 support for the idxd driver.

> From: Jason Gunthorpe <jgg@...lanox.com>
> Sent: Monday, April 27, 2020 9:22 PM
> 
> On Mon, Apr 27, 2020 at 07:19:39AM -0600, Alex Williamson wrote:
> 
> > > 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,
> 
> Look around vidxd_do_command()
> 
> If I understand this flow properly..
> 

Hi, Jason,

I guess the 2000 lines mostly refer to the changes in mdev.c and vdev.c. 
We did a break-down among them:

1) ~150 LOC for vdev initialization
2) ~150 LOC for cfg space emulation
3) ~230 LOC for mmio r/w emulation
4) ~500 LOC for controlling the work queue (vidxd_do_command), 
triggered by write emulation of IDXD_CMD_OFFSET register
5) the remaining lines are all about vfio-mdev registration/callbacks,
for reporting mmio/irq resource, eventfd, mmap, etc.

1/2/3) are pure device emulation, which counts for ~500 LOC. 

4) needs be in the kernel regardless of which uAPI is used, because it
talks to the physical work queue (enable, disable, drain, abort, reset, etc.)

Then if just talking about ~500 LOC emulation code left in the kernel, 
is it still a big concern to you? 😊

Thanks
Kevin