From: Matthew Rosato <mjrosato@linux.ibm.com>
To: Niklas Schnelle <schnelle@linux.ibm.com>,
Joerg Roedel <joro@8bytes.org>, Will Deacon <will@kernel.org>,
Wenjia Zhang <wenjia@linux.ibm.com>,
Robin Murphy <robin.murphy@arm.com>,
Jason Gunthorpe <jgg@ziepe.ca>
Cc: Gerd Bayer <gbayer@linux.ibm.com>,
Julian Ruess <julianr@linux.ibm.com>,
Pierre Morel <pmorel@linux.ibm.com>,
Alexandra Winter <wintera@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Sven Schnelle <svens@linux.ibm.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Hector Martin <marcan@marcan.st>, Sven Peter <sven@svenpeter.dev>,
Alyssa Rosenzweig <alyssa@rosenzweig.io>,
David Woodhouse <dwmw2@infradead.org>,
Lu Baolu <baolu.lu@linux.intel.com>,
Andy Gross <agross@kernel.org>,
Bjorn Andersson <andersson@kernel.org>,
Konrad Dybcio <konrad.dybcio@linaro.org>,
Yong Wu <yong.wu@mediatek.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@collabora.com>,
Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
Orson Zhai <orsonzhai@gmail.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Chunyan Zhang <zhang.lyra@gmail.com>,
Chen-Yu Tsai <wens@csie.org>,
Jernej Skrabec <jernej.skrabec@gmail.com>,
Samuel Holland <samuel@sholland.org>,
Thierry Reding <thierry.reding@gmail.com>,
Krishna Reddy <vdumpa@nvidia.com>,
Jonathan Hunter <jonathanh@nvidia.com>,
Jonathan Corbet <corbet@lwn.net>,
linux-s390@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
asahi@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
linux-arm-msm@vger.kernel.org,
linux-mediatek@lists.infradead.org, linux-sunxi@lists.linux.dev,
linux-tegra@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH v13 4/6] iommu/s390: Disable deferred flush for ISM devices
Date: Fri, 29 Sep 2023 08:56:30 -0400 [thread overview]
Message-ID: <2513a9d4-ac92-2e50-4861-bb65465cf1ae@linux.ibm.com> (raw)
In-Reply-To: <20230928-dma_iommu-v13-4-9e5fc4dacc36@linux.ibm.com>
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@linux.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@linux.ibm.com>
next prev parent reply other threads:[~2023-09-29 12:57 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-28 14:31 [PATCH v13 0/6] iommu/dma: s390 DMA API conversion and optimized IOTLB flushing Niklas Schnelle
2023-09-28 14:31 ` [PATCH v13 1/6] iommu: Allow .iotlb_sync_map to fail and handle s390's -ENOMEM return Niklas Schnelle
2023-09-28 14:31 ` [PATCH v13 2/6] s390/pci: prepare is_passed_through() for dma-iommu Niklas Schnelle
2023-09-28 14:31 ` [PATCH v13 3/6] s390/pci: Use dma-iommu layer Niklas Schnelle
2023-09-28 14:31 ` [PATCH v13 4/6] iommu/s390: Disable deferred flush for ISM devices Niklas Schnelle
2023-09-29 12:56 ` Matthew Rosato [this message]
2023-09-28 14:31 ` [PATCH v13 5/6] iommu/dma: Allow a single FQ in addition to per-CPU FQs Niklas Schnelle
2023-09-28 14:31 ` [PATCH v13 6/6] iommu/dma: Use a large flush queue and timeout for shadow_on_flush Niklas Schnelle
2023-10-02 6:59 ` [PATCH v13 0/6] iommu/dma: s390 DMA API conversion and optimized IOTLB flushing Joerg Roedel
2023-10-04 8:54 ` Niklas Schnelle
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