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

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Date:   Mon, 27 Apr 2020 08:18:41 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        "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.

On Mon, 27 Apr 2020 10:22:18 -0300
Jason Gunthorpe <jgg@...lanox.com> wrote:

> 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..

I've only glanced at it, but that's called in response to a write to
MMIO space on the device, so it's implementing a device specific
register.  Are you asking that PCI config space be done in userspace
or any sort of device emulation?  The assumption with mdev is that we
need emulation in the host kernel because we need a trusted entity to
mediate device access and interact with privileged portion of the
device control.  Thanks,

Alex