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Message-ID: <2513a9d4-ac92-2e50-4861-bb65465cf1ae@linux.ibm.com> Date: Fri, 29 Sep 2023 08:56:30 -0400 From: Matthew Rosato <mjrosato@...ux.ibm.com> To: Niklas Schnelle <schnelle@...ux.ibm.com>, Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, Wenjia Zhang <wenjia@...ux.ibm.com>, Robin Murphy <robin.murphy@....com>, Jason Gunthorpe <jgg@...pe.ca> Cc: Gerd Bayer <gbayer@...ux.ibm.com>, Julian Ruess <julianr@...ux.ibm.com>, Pierre Morel <pmorel@...ux.ibm.com>, Alexandra Winter <wintera@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>, Suravee Suthikulpanit <suravee.suthikulpanit@....com>, Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>, Alyssa Rosenzweig <alyssa@...enzweig.io>, David Woodhouse <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>, Andy Gross <agross@...nel.org>, Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, Yong Wu <yong.wu@...iatek.com>, Matthias Brugger <matthias.bgg@...il.com>, AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Gerald Schaefer <gerald.schaefer@...ux.ibm.com>, Orson Zhai <orsonzhai@...il.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, Chunyan Zhang <zhang.lyra@...il.com>, Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, Thierry Reding <thierry.reding@...il.com>, Krishna Reddy <vdumpa@...dia.com>, Jonathan Hunter <jonathanh@...dia.com>, Jonathan Corbet <corbet@....net>, linux-s390@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, linux-arm-msm@...r.kernel.org, linux-mediatek@...ts.infradead.org, linux-sunxi@...ts.linux.dev, linux-tegra@...r.kernel.org, linux-doc@...r.kernel.org Subject: Re: [PATCH v13 4/6] iommu/s390: Disable deferred flush for ISM devices On 9/28/23 10:31 AM, Niklas Schnelle wrote: > ISM devices are virtual PCI devices used for cross-LPAR communication. > Unlike real PCI devices ISM devices do not use the hardware IOMMU but > inspects IOMMU translation tables directly on IOTLB flush (s390 RPCIT > instruction). > > ISM devices keep their DMA allocations static and only very rarely DMA > unmap at all. For each IOTLB flush that occurs after unmap the ISM > devices will however inspect the area of the IOVA space indicated by the > flush. This means that for the global IOTLB flushes used by the flush > queue mechanism the entire IOVA space would be inspected. In principle > this would be fine, albeit potentially unnecessarily slow, it turns out > however that ISM devices are sensitive to seeing IOVA addresses that are > currently in use in the IOVA range being flushed. Seeing such in-use > IOVA addresses will cause the ISM device to enter an error state and > become unusable. > > Fix this by claiming IOMMU_CAP_DEFERRED_FLUSH only for non-ISM devices. > This makes sure IOTLB flushes only cover IOVAs that have been unmapped > and also restricts the range of the IOTLB flush potentially reducing > latency spikes. > > Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com> Looks like my review tag from v12 got dropped on accident -- no changes since prior version and still looks good to me so Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>
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