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

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Message-ID: <87tumj423u.ffs@nanos.tec.linutronix.de>
Date:   Mon, 31 May 2021 12:41:25 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jason Gunthorpe <jgg@...dia.com>, Dave Jiang <dave.jiang@...el.com>
Cc:     alex.williamson@...hat.com, kwankhede@...dia.com, 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 13:39, Jason Gunthorpe wrote:
> 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.

The general expectation is that the MSI irqdomain is retrievable from
struct device for any device which supports MSI.

Thanks,

        tglx