Re: [PATCH v3 2/7] iommu: Allow .iotlb_sync_map to fail and handle s390's -ENOMEM return

[Niklas Schnelle]

On Tue, 2023-01-03 at 09:16 +0100, Niklas Schnelle wrote:
> On Mon, 2023-01-02 at 19:25 +0100, Alexandra Winter wrote:
> > 
> > On 02.01.23 12:56, Niklas Schnelle wrote:
> > > On s390 .iotlb_sync_map is used to sync mappings to an underlying
> > > hypervisor by letting the hypervisor inspect the synced IOVA range and
> > > updating its shadow table. This however means that it can fail as the
> > > hypervisor may run out of resources. This can be due to the hypervisor
> > > being unable to pin guest pages, due to a limit on concurrently mapped
> > > addresses such as vfio_iommu_type1.dma_entry_limit or other resources.
> > > Either way such a failure to sync a mapping should result in
> > > a DMA_MAPPING_EROR.
> > > 
> > > Now especially when running with batched IOTLB flushes for unmap it may
> > > be that some IOVAs have already been invalidated but not yet synced via
> > > .iotlb_sync_map. Thus if the hypervisor indicates running out of
> > > resources, first do a global flush allowing the hypervisor to free
> > > resources associated with these mappings and only if that also fails
> > > report this error to callers.
> > > 
> > > Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> > > ---
> > Just a small typo, I noticed
> > [...]
> 
> You mean the misspelled DMA_MAPPING_ERROR, right? Either way I did edit
> the commit message for a bit more clarity on some of the details:
> 
> On s390 when using a paging hypervisor, .iotlb_sync_map is used to sync
> mappings by letting the hypervisor inspect the synced IOVA range and
> updating a shadow table. This however means that .iotlb_sync_map can
> fail as the hypervisor may run out of resources while doing the sync.
> This can be due to the hypervisor being unable to pin guest pages, due
> to a limit on mapped addresses such as vfio_iommu_type1.dma_entry_limit
> or lack of other resources. Either way such a failure to sync a mapping
> should result in a DMA_MAPPING_ERROR.
> 
> Now especially when running with batched IOTLB flushes for unmap it may
> be that some IOVAs have already been invalidated but not yet synced via
> .iotlb_sync_map. Thus if the hypervisor indicates running out of
> resources, first do a global flush allowing the hypervisor to free
> resources associated with these mappings as well a retry creating the
> new mappings and only if that also fails report this error to callers.
> 
> 
> 
> > > diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
> > > index ed33c6cce083..6ba38b4f5b37 100644
> > > --- a/drivers/iommu/s390-iommu.c
> > > +++ b/drivers/iommu/s390-iommu.c
> > > @@ -210,6 +210,14 @@ static void s390_iommu_release_device(struct device *dev)
> > >  		__s390_iommu_detach_device(zdev);
> > >  }
> > >  
> > > +
> > > +static int zpci_refresh_all(struct zpci_dev *zdev)
> > > +{
> > > +	return zpci_refresh_trans((u64)zdev->fh << 32, zdev->start_dma,
> > > +				  zdev->end_dma - zdev->start_dma + 1);
> > > +
> > > +}
> > > +
> > >  static void s390_iommu_flush_iotlb_all(struct iommu_domain *domain)
> > >  {
> > >  	struct s390_domain *s390_domain = to_s390_domain(domain);
> > > @@ -217,8 +225,7 @@ static void s390_iommu_flush_iotlb_all(struct iommu_domain *domain)
> > >  
> > >  	rcu_read_lock();
> > >  	list_for_each_entry_rcu(zdev, &s390_domain->devices, iommu_list) {
> > > -		zpci_refresh_trans((u64)zdev->fh << 32, zdev->start_dma,
> > > -				   zdev->end_dma - zdev->start_dma + 1);
> > > +		zpci_refresh_all(zdev);
> > >  	}
> > >  	rcu_read_unlock();
> > >  }
> > > @@ -242,20 +249,32 @@ static void s390_iommu_iotlb_sync(struct iommu_domain *domain,
> > >  	rcu_read_unlock();
> > >  }
> > >  
> > > -static void s390_iommu_iotlb_sync_map(struct iommu_domain *domain,
> > > +static int s390_iommu_iotlb_sync_map(struct iommu_domain *domain,
> > >  				      unsigned long iova, size_t size)
> > >  {
> > >  	struct s390_domain *s390_domain = to_s390_domain(domain);
> > >  	struct zpci_dev *zdev;
> > > +	int ret = 0;
> > >  
> > >  	rcu_read_lock();
> > >  	list_for_each_entry_rcu(zdev, &s390_domain->devices, iommu_list) {
> > >  		if (!zdev->tlb_refresh)
> > >  			continue;
> > > -		zpci_refresh_trans((u64)zdev->fh << 32,
> > > -				   iova, size);
> > > +		ret = zpci_refresh_trans((u64)zdev->fh << 32,
> > > +					 iova, size);
> > > +		/*
> > > +		 * let the hypervisor disover invalidated entries
> > 			typo: s/disover/discover/g

I'm blind, missed this one. Added the change now.

> > > +		 * allowing it to free IOVAs and unpin pages
> > > +		 */
> > > +		if (ret == -ENOMEM) {
> > > +			ret = zpci_refresh_all(zdev);
> > > +			if (ret)
> > > +				break;
> > > +		}
> > >  	}
> > >  	rcu_read_unlock();
> > > +
> > > +	return ret;
> > >  }
> > >  
> > >  static int s390_iommu_validate_trans(struct s390_domain *s390_domain,
> > [...]
>