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

Alexandra Winter
2023-01-02T18:26:03Z

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@linux.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, …