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authorNishanth Aravamudan <nacc at linux.vnet.ibm.com>2015-11-24 19:55:05 +0300
committerJens Axboe <axboe@fb.com>2015-11-25 01:05:51 +0300
commitc5c9f25b98a568451d665afe4aeefe17bf9f2995 (patch)
treec1e8dde2a60c47c00f2cd9a97db44723e1acc29c /drivers/irqchip
parent6ffeba9607343f15303a399bc402a538800d89d9 (diff)
downloadlinux-c5c9f25b98a568451d665afe4aeefe17bf9f2995.tar.xz
NVMe: default to 4k device page size
We received a bug report recently when DDW (64-bit direct DMA on Power) is not enabled for NVMe devices. In that case, we fall back to 32-bit DMA via the IOMMU, which is always done via 4K TCEs (Translation Control Entries). The NVMe device driver, though, assumes that the DMA alignment for the PRP entries will match the device's page size, and that the DMA aligment matches the kernel's page aligment. On Power, the the IOMMU page size, as mentioned above, can be 4K, while the device can have a page size of 8K, while the kernel has a page size of 64K. This eventually trips the BUG_ON in nvme_setup_prps(), as we have a 'dma_len' that is a multiple of 4K but not 8K (e.g., 0xF000). In this particular case of page sizes, we clearly want to use the IOMMU's page size in the driver. And generally, the NVMe driver in this function should be using the IOMMU's page size for the default device page size, rather than the kernel's page size. There is not currently an API to obtain the IOMMU's page size across all architectures and in the interest of a stop-gap fix to this functional issue, default the NVMe device page size to 4K, with the intent of adding such an API and implementation across all architectures in the next merge window. With the functionally equivalent v3 of this patch, our hardware test exerciser survives when using 32-bit DMA; without the patch, the kernel will BUG within a few minutes. Signed-off-by: Nishanth Aravamudan <nacc at linux.vnet.ibm.com> Signed-off-by: Jens Axboe <axboe@fb.com>
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