linux-kernel - Re: [PATCH v4 2/7] iommu: Allow .iotlb_sync_map to fail and handle s390's -ENOMEM return

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Message-ID: <849e5a33-519c-be63-7400-2843a8440620@linux.ibm.com>
Date:   Tue, 17 Jan 2023 10:10:07 -0500
From:   Matthew Rosato <mjrosato@...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:     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 v4 2/7] iommu: Allow .iotlb_sync_map to fail and handle
 s390's -ENOMEM return

On 1/4/23 7:05 AM, Niklas Schnelle wrote:
> 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.
> 
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>

Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>