linux-kernel - Re: [PATCH v6 15/20] vfio/mdev: idxd: ims domain setup for the vdcm

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Message-ID: <20210523235023.GL1002214@nvidia.com>
Date:   Sun, 23 May 2021 20:50:23 -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 15/20] vfio/mdev: idxd: ims domain setup for the vdcm

On Fri, May 21, 2021 at 05:20:37PM -0700, Dave Jiang wrote:
> @@ -77,8 +80,18 @@ int idxd_mdev_host_init(struct idxd_device *idxd, struct mdev_driver *drv)
>  		return rc;
>  	}
>  
> +	ims_info.max_slots = idxd->ims_size;
> +	ims_info.slots = idxd->reg_base + idxd->ims_offset;
> +	idxd->ims_domain = pci_ims_array_create_msi_irq_domain(idxd->pdev, &ims_info);
> +	if (!idxd->ims_domain) {
> +		dev_warn(dev, "Fail to acquire IMS domain\n");
> +		iommu_dev_disable_feature(dev, IOMMU_DEV_FEAT_AUX);
> +		return -ENODEV;
> +	}

I'm quite surprised that every mdev doesn't create its own ims_domain
in its probe function.

This places a global total limit on the # of vectors which makes me
ask what was the point of using IMS in the first place ?

The entire idea for IMS was to make the whole allocation system fully
dynamic based on demand.

>  	rc = mdev_register_device(dev, drv);
>  	if (rc < 0) {
> +		irq_domain_remove(idxd->ims_domain);
>  		iommu_dev_disable_feature(dev, IOMMU_DEV_FEAT_AUX);
>  		return rc;
>  	}

This really wants a goto error unwind

Jason