linux-kernel - Re: [PATCH v5 1/6] iommu/s390: Fix duplicate domain attachments

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Date:   Fri, 07 Oct 2022 08:55:01 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>, iommu@...ts.linux.dev
Cc:     linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, joro@...tes.org, will@...nel.org,
        robin.murphy@....com, jgg@...dia.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/6] iommu/s390: Fix duplicate domain attachments

On Thu, 2022-10-06 at 17:02 -0400, Matthew Rosato wrote:
> On 10/6/22 10:46 AM, Niklas Schnelle wrote:
> > Since commit fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev
> > calls") we can end up with duplicates in the list of devices attached to
> > a domain. This is inefficient and confusing since only one domain can
> > actually be in control of the IOMMU translations for a device. Fix this
> > by detaching the device from the previous domain, if any, on attach.
> > Add a WARN_ON() in case we still have attached devices on freeing the
> > domain. While here remove the re-attach on failure dance as it was
> > determined to be unlikely to help and may confuse debug and recovery.
> > 
> > Fixes: fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev calls")
> > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> > ---
> > v4->v5:
> > - Unregister IOAT and set zdev->dma_table on error (Matt)
> > 
> ...
> 
> >  static int s390_iommu_attach_device(struct iommu_domain *domain,
> >  				    struct device *dev)
> >  {
> > @@ -90,7 +116,7 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
> >  	struct zpci_dev *zdev = to_zpci_dev(dev);
> >  	struct s390_domain_device *domain_device;
> >  	unsigned long flags;
> > -	int cc, rc;
> > +	int cc, rc = 0;
> >  
> >  	if (!zdev)
> >  		return -ENODEV;
> > @@ -99,23 +125,17 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
> >  	if (!domain_device)
> >  		return -ENOMEM;
> >  
> > -	if (zdev->dma_table && !zdev->s390_domain) {
> > -		cc = zpci_dma_exit_device(zdev);
> > -		if (cc) {
> > -			rc = -EIO;
> > -			goto out_free;
> > -		}
> > -	}
> > -
> >  	if (zdev->s390_domain)
> > -		zpci_unregister_ioat(zdev, 0);
> > +		__s390_iommu_detach_device(zdev);
> > +	else if (zdev->dma_table)
> > +		zpci_dma_exit_device(zdev);
> >  
> >  	zdev->dma_table = s390_domain->dma_table;
> >  	cc = zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
> >  				virt_to_phys(zdev->dma_table));
> >  	if (cc) {
> >  		rc = -EIO;
> > -		goto out_restore;
> > +		goto out_free;
> >  	}
> 
> Hmm, with this we will leave attach_dev with a zdev->dma_table associated with this domain (not one generated via zpci_dma_init_device) and zdev->s390_domain == 0.  Won't this cause both s390_domain_free and zpci_dma_exit_device() to try and free the same dma table?
> 
> I think we also have to leave with a NULL zdev->dma_table in this case too (you technically could skip the zpci_unregister_ioat)


Argh you're right. This is I think a a bad rebase, in v4 I had the
zpci_register_ioat() use s390_domain->dma_table and only set zdev-
>dma_table after that succeeded. I seem to have lost that part
somewhere along the way. With that we zdev->dma_table would be NULL and
all would be good.

> 
> >  
> >  	spin_lock_irqsave(&s390_domain->list_lock, flags);
> > @@ -127,9 +147,9 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
> >  	/* Allow only devices with identical DMA range limits */
> >  	} else if (domain->geometry.aperture_start != zdev->start_dma ||
> >  		   domain->geometry.aperture_end != zdev->end_dma) {
> > -		rc = -EINVAL;
> >  		spin_unlock_irqrestore(&s390_domain->list_lock, flags);
> > -		goto out_restore;
> > +		rc = -EINVAL;
> > +		goto out_unregister;
> >  	}
> >  	domain_device->zdev = zdev;
> >  	zdev->s390_domain = s390_domain;
> > @@ -138,14 +158,9 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
> >  
> >  	return 0;
> >  
> > -out_restore:
> > -	if (!zdev->s390_domain) {
> > -		zpci_dma_init_device(zdev);
> > -	} else {
> > -		zdev->dma_table = zdev->s390_domain->dma_table;
> > -		zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
> > -				   virt_to_phys(zdev->dma_table));
> > -	}
> > +out_unregister:
> > +	zpci_unregister_ioat(zdev, 0);
> > +	zdev->dma_table = NULL;
> >  out_free:
> >  	kfree(domain_device);
> >