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

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Message-ID: <Y7P02dYnvGgbqA2C@osiris>
Date:   Tue, 3 Jan 2023 10:26:49 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Alexandra Winter <wintera@...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>,
        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,
        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 Tue, Jan 03, 2023 at 09:16:22AM +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@...ux.ibm.com>
> > > ---
> > Just a small typo, I noticed
> > [...]
> 
> You mean the misspelled DMA_MAPPING_ERROR, right? Either way I did edit

I think Alexandra meant the below:

> > > +		/*
> > > +		 * let the hypervisor disover invalidated entries
> > 			typo: s/disover/discover/g

Now you know why I always complain when people do full quotes and not
trim replies to relevant parts.
It is sometimes very hard to spot comments :)