linux-kernel - Re: [PATCH v6 05/20] vfio: mdev: common lib code for setting up Interrupt Message Store

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Message-ID: <20210528163906.GN1002214@nvidia.com>
Date:   Fri, 28 May 2021 13:39:06 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     alex.williamson@...hat.com, kwankhede@...dia.com,
        tglx@...utronix.de, vkoul@...nel.org, megha.dey@...el.com,
        jacob.jun.pan@...el.com, ashok.raj@...el.com, yi.l.liu@...el.com,
        baolu.lu@...el.com, kevin.tian@...el.com, sanjay.k.kumar@...el.com,
        tony.luck@...el.com, dan.j.williams@...el.com,
        eric.auger@...hat.com, pbonzini@...hat.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v6 05/20] vfio: mdev: common lib code for setting up
 Interrupt Message Store

On Fri, May 28, 2021 at 09:37:56AM -0700, Dave Jiang wrote:
> 
> On 5/28/2021 5:21 AM, Jason Gunthorpe wrote:
> > On Thu, May 27, 2021 at 06:49:59PM -0700, Dave Jiang wrote:
> > > > > +static int mdev_msix_enable(struct mdev_irq *mdev_irq, int nvec)
> > > > > +{
> > > > > +	struct mdev_device *mdev = irq_to_mdev(mdev_irq);
> > > > > +	struct device *dev;
> > > > > +	int rc;
> > > > > +
> > > > > +	if (nvec != mdev_irq->num)
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	if (mdev_irq->ims_num) {
> > > > > +		dev = &mdev->dev;
> > > > > +		rc = msi_domain_alloc_irqs(dev_get_msi_domain(dev), dev, mdev_irq->ims_num);
> > > > Huh? The PCI device should be the only device touching IRQ stuff. I'm
> > > > nervous to see you mix in the mdev struct device into this function.
> > > As we talked about in the other thread. We have a single IMS domain per
> > > device. The domain is set to the mdev 'struct device' and we allocate the
> > > vectors to each mdev 'struct device' so we can manage those IMS vectors
> > > specifically for that mdev.
> > That is not the point, I'm asking if you should be calling
> > dev_set_msi_domain(mdev) at all
> 
> I'm not familiar with the standard way of doing this. Should I not set the
> domain to the mdev 'struct device' because I can have multiple mdev using
> the same domain? With the domain set, I am able to retrieve it and call the
> msi_domain_alloc_irqs() in common code. Alternatively we can pass in the
> domain during init and not rely on dev->msi_

Honestly, I don't know. I would prefer Thomas confirm what is the
correct way to use the msi_domain as IDXD is going to be the reference
everyone copies.

Jason