Re: [PATCH v5 3/6] iommu/s390: Fix potential s390_domain aperture shrinking

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Thu, 2022-10-06 at 17:02 -0400, Matthew Rosato wrote:
> On 10/6/22 10:46 AM, Niklas Schnelle wrote:
> > The s390 IOMMU driver currently sets the IOMMU domain's aperture to
> > match the device specific DMA address range of the device that is first
> > attached. This is not ideal. For one if the domain has no device
> > attached in the meantime the aperture could be shrunk allowing
> > translations outside the aperture to exist in the translation tables.
> > Also this is a bit of a misuse of the aperture which really should
> > describe what addresses can be translated and not some device specific
> > limitations.
> > 
> > Instead of misusing the aperture like this we can instead create
> > reserved ranges for the ranges inaccessible to the attached devices
> > allowing devices with overlapping ranges to still share an IOMMU domain.
> > This also significantly simplifies s390_iommu_attach_device() allowing
> > us to move the aperture check to the beginning of the function and
> > removing the need to hold the device list's lock to check the aperture.
> > 
> > As we then use the same aperture for all domains and it only depends on
> > the table properties we can already check zdev->start_dma/end_dma at
> > probe time and turn the check on attach into a WARN_ON().
> > 
> > Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> > Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> 
> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
> 
> > ---
> > v4->v5:
> > - Make aperture check in attach a WARN_ON() and fail in probe if
> >   zdev->start_dma/end_dma doesn't git in aperture  (Jason)
> > 
> >  drivers/iommu/s390-iommu.c | 65 +++++++++++++++++++++++++-------------
> >  1 file changed, 43 insertions(+), 22 deletions(-)
> > 
> > diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
> > index 9b3ae4b14636..1f6c9bee9a80 100644
> > --- a/drivers/iommu/s390-iommu.c
> > +++ b/drivers/iommu/s390-iommu.c
> > @@ -62,6 +62,9 @@ static struct iommu_domain *s390_domain_alloc(unsigned domain_type)
> >  		kfree(s390_domain);
> >  		return NULL;
> >  	}
> > +	s390_domain->domain.geometry.force_aperture = true;
> > +	s390_domain->domain.geometry.aperture_start = 0;
> > +	s390_domain->domain.geometry.aperture_end = ZPCI_TABLE_SIZE_RT - 1;
> >  
> >  	spin_lock_init(&s390_domain->dma_table_lock);
> >  	spin_lock_init(&s390_domain->list_lock);
> > @@ -102,46 +105,32 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
> >  	struct s390_domain *s390_domain = to_s390_domain(domain);
> >  	struct zpci_dev *zdev = to_zpci_dev(dev);
> >  	unsigned long flags;
> > -	int cc, rc = 0;
> > +	int cc;
> >  
> >  	if (!zdev)
> >  		return -ENODEV;
> >  
> > +	WARN_ON(domain->geometry.aperture_start > zdev->end_dma ||
> > +		domain->geometry.aperture_end < zdev->start_dma);
> > +

I think this one should still return with -EINVAL.

> >  	if (zdev->s390_domain)
> >  		__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));
> > +				virt_to_phys(s390_domain->dma_table));
> >  	if (cc)
> >  		return -EIO;
> >  
> > -	spin_lock_irqsave(&s390_domain->list_lock, flags);
> > -	/* First device defines the DMA range limits */
> > -	if (list_empty(&s390_domain->devices)) {
> > -		domain->geometry.aperture_start = zdev->start_dma;
> > -		domain->geometry.aperture_end = zdev->end_dma;
> > -		domain->geometry.force_aperture = true;
> > -	/* Allow only devices with identical DMA range limits */
> > -	} else if (domain->geometry.aperture_start != zdev->start_dma ||
> > -		   domain->geometry.aperture_end != zdev->end_dma) {
> > -		spin_unlock_irqrestore(&s390_domain->list_lock, flags);
> > -		rc = -EINVAL;
> > -		goto out_unregister;
> > -	}
> > +	zdev->dma_table = s390_domain->dma_table;
> >  	zdev->s390_domain = s390_domain;
> > +
> > +	spin_lock_irqsave(&s390_domain->list_lock, flags);
> >  	list_add(&zdev->iommu_list, &s390_domain->devices);
> >  	spin_unlock_irqrestore(&s390_domain->list_lock, flags);
> >  
> >  	return 0;
> > -
> > -out_unregister:
> > -	zpci_unregister_ioat(zdev, 0);
> > -	zdev->dma_table = NULL;
> > -
> > -	return rc;
> >  }
> >  
> > 
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