linux-kernel - Re: [PATCH 4/4] dmaengine/idxd: Re-enable kernel workqueue under DMA API

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Message-ID: <ZACdTG4QZSHF2QRj@nvidia.com>
Date:   Thu, 2 Mar 2023 08:57:48 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>
Subject: Re: [PATCH 4/4] dmaengine/idxd: Re-enable kernel workqueue under DMA
 API

On Thu, Mar 02, 2023 at 09:47:00AM +0000, Tian, Kevin wrote:
> > From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > Sent: Thursday, March 2, 2023 9:00 AM
> > 
> >  static int idxd_enable_system_pasid(struct idxd_device *idxd)
> >  {
> > -	return -EOPNOTSUPP;
> > +	struct pci_dev *pdev = idxd->pdev;
> > +	struct device *dev = &pdev->dev;
> > +	struct iommu_domain *domain;
> > +	union gencfg_reg gencfg;
> > +	ioasid_t pasid;
> > +	int ret;
> > +
> > +	domain = iommu_get_domain_for_dev(dev);
> > +	if (!domain || domain->type == IOMMU_DOMAIN_BLOCKED)
> > +		return -EPERM;
> 
> what about UNMANAGED?

Why are we checking this anyhow?

Get the domain the DMA API is using and feed it to
iommu_attach_device_pasid(). If the driver can't mirror the DMA API's
domain onto the PASID then it will just fail the attach. A domain
cannot even be NULL on x86.

Jason