Recent commit 52fde2c07da6 ("nvme: set dma alignment to dword") has caused a regression on our platform. It turned out that the nvme_get_log() method invocation caused the nvme_hwmon_data structure instance corruption. In particular the nvme_hwmon_data.ctrl pointer was overwritten either with zeros or with garbage. After some research we discovered that the problem happened even before the actual NVME DMA execution, but during the buffer mapping. Since our platform is DMA-noncoherent, the mapping implied the cache-line invalidations or write-backs depending on the DMA-direction parameter. In case of the NVME SMART log getting the DMA was performed from-device-to-memory, thus the cache-invalidation was activated during the buffer mapping. Since the log-buffer isn't cache-line aligned, the cache-invalidation caused the neighbour data to be discarded. The neighbouring data turned to be the data surrounding the buffer in the framework of the nvme_hwmon_data structure. In order to fix that we need to make sure that the whole log-buffer is defined within the cache-line-aligned memory region so the cache-invalidation procedure wouldn't involve the adjacent data. One of the option to guarantee that is to kmalloc the DMA-buffer [1]. Seeing the rest of the NVME core driver prefer that method it has been chosen to fix this problem too. Note after a deeper researches we found out that the denoted commit wasn't a root cause of the problem. It just revealed the invalidity by activating the DMA-based NVME SMART log getting performed in the framework of the NVME hwmon driver. The problem was here since the initial commit of the driver. [1] Documentation/core-api/dma-api-howto.rst Fixes: 400b6a7b13a3 ("nvme: Add hardware monitoring support") Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> Signed-off-by: Christoph Hellwig <hch@lst.de>
Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.
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