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

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Date:   Mon, 2 Jan 2023 19:25:22 +0100
From:   Alexandra Winter <wintera@...ux.ibm.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>
Cc:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>, iommu@...ts.linux.dev,
        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, linux-kernel@...r.kernel.org,
        Julian Ruess <julianr@...ux.ibm.com>
Subject: Re: [PATCH v3 2/7] iommu: Allow .iotlb_sync_map to fail and handle
 s390's -ENOMEM return



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@...ux.ibm.com>
> ---
Just a small typo, I noticed
[...]
> 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
> +		 * 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,
[...]