[Sorry, subject should have been 0/7!] On 23.10.2015 [13:54:20 -0700], Nishanth Aravamudan wrote: > 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, and generally, we want to use the IOMMU's page > size for the default device page size, rather than the kernel's page > size. > > This series consists of five patches: > > 1) add a generic dma_get_page_shift implementation that just returns > PAGE_SHIFT > 2) override the generic implementation on Power to use the IOMMU table's > page shift if available > 3) allow further specific overriding on power with machdep platform > overrides > 4) use the machdep override on pseries, as the DDW code puts the TCE > shift in a special property and there is no IOMMU table available > 5) move some sparc code around to make IOMMU_PAGE_SHIFT available in > include/asm > 6) override the generic implementation on sparce to use IOMMU_PAGE_SHIFT > 7) leverage the new API in the NVMe driver > > With these patches, a NVMe device survives our internal hardware > exerciser; the kernel BUGs within a few seconds without the patch. > > arch/powerpc/include/asm/dma-mapping.h | 3 +++ > arch/powerpc/include/asm/machdep.h | 3 ++- > arch/powerpc/kernel/dma.c | 11 +++++++++++ > arch/powerpc/platforms/pseries/iommu.c | 36 ++++++++++++++++++++++++++++++++++++ > arch/sparc/include/asm/dma-mapping.h | 8 ++++++++ > arch/sparc/include/asm/iommu_common.h | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ > arch/sparc/kernel/iommu.c | 2 +- > arch/sparc/kernel/iommu_common.h | 51 --------------------------------------------------- > arch/sparc/kernel/pci_psycho.c | 2 +- > arch/sparc/kernel/pci_sabre.c | 2 +- > arch/sparc/kernel/pci_schizo.c | 2 +- > arch/sparc/kernel/pci_sun4v.c | 2 +- > arch/sparc/kernel/psycho_common.c | 2 +- > arch/sparc/kernel/sbus.c | 3 +-- > drivers/block/nvme-core.c | 3 ++- > include/linux/dma-mapping.h | 7 +++++++ > 16 files changed, 127 insertions(+), 61 deletions(-) > > v1 -> v2: > Based upon feedback from Christoph Hellwig, rather than using an > arch-specific hack, expose the DMA page shift via a generic DMA API and > override it on Power as needed. > v2 -> v3: > Based upon feedback from Christoph Hellwig, put the generic > implementation in include/linux/dma-mapping.h, since not all archs use > include/asm-generic/dma-mapping-common.h. > Add sparc implementation, as that arch seems to have a different IOMMU > page size. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
