On Fri, 2016-06-10 at 10:03 -0300, Mauricio Faria de Oliveira wrote:
> This prevents flooding the logs with 'iommu_alloc failed' messages
> while I/O is performed (normally) to very fast devices (e.g. NVMe).
>
> That error is not necessarily a problem; device drivers can retry
> later / reschedule the requests for which the allocation failed,
> and handle things gracefully for the caller stack on top of them.
>
> This helps at least with NVMe devices without "64-bit"/direct DMA
> window scenarios (e.g., systems with more than a few terabytes of
> memory, on which DDW cannot be enabled, currently), where just an
> 'dd' command can trigger errors.
I'm not fan of this. This is a very useful message to diagnose why,
for example, your network adapter is not working properly.
A lot of drivers don't deal well with IOMMU errors.
The fact that NVME trigger these is a problem that needs to be solved
differently.
Cheers,
Ben.
>
> # dd if=/dev/zero of=/dev/nvme0n1p1 bs=64k count=512k
> <...>
> # echo $?
> 0
>
> # dmesg
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c000000151c90000 npages 16
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c000000151c90000 npages 16
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c000000151c90000 npages 16
> <...>
> ppc_iommu_map_sg: 8186 callbacks suppressed
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c0000000fa5c0000 npages 16
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c000000100440000 npages 16
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c000000100440000 npages 16
> <...>
> ppc_iommu_map_sg: 5707 callbacks suppressed
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c0000000b5f50000 npages 16
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c0000000b5c60000 npages 16
> nvme 0000:00:06.0: iommu_alloc failed, tbl c0000001fa67c520 vaddr
> c0000000b4b30000 npages 16
> <...>
>
> Tested on next-20160609.
>
> Signed-off-by: Mauricio Faria de Oliveira <mauri...@linux.vnet.ibm.co
> m>
> ---
> arch/powerpc/kernel/iommu.c | 15 ++++++---------
> 1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/kernel/iommu.c
> b/arch/powerpc/kernel/iommu.c
> index a8e3490..b585bdc 100644
> --- a/arch/powerpc/kernel/iommu.c
> +++ b/arch/powerpc/kernel/iommu.c
> @@ -479,10 +479,9 @@ int ppc_iommu_map_sg(struct device *dev, struct
> iommu_table *tbl,
>
> /* Handle failure */
> if (unlikely(entry == DMA_ERROR_CODE)) {
> - if (printk_ratelimit())
> - dev_info(dev, "iommu_alloc failed,
> tbl %p "
> - "vaddr %lx npages %lu\n",
> tbl, vaddr,
> - npages);
> + dev_dbg_ratelimited(dev, "iommu_alloc
> failed, tbl %p "
> + "vaddr %lx npages %lu\n", tbl,
> vaddr,
> + npages);
> goto failure;
> }
>
> @@ -776,11 +775,9 @@ dma_addr_t iommu_map_page(struct device *dev,
> struct iommu_table *tbl,
> mask >> tbl->it_page_shift,
> align,
> attrs);
> if (dma_handle == DMA_ERROR_CODE) {
> - if (printk_ratelimit()) {
> - dev_info(dev, "iommu_alloc failed,
> tbl %p "
> - "vaddr %p npages %d\n",
> tbl, vaddr,
> - npages);
> - }
> + dev_dbg_ratelimited(dev, "iommu_alloc
> failed, tbl %p "
> + "vaddr %p npages %d\n", tbl, vaddr,
> + npages);
> } else
> dma_handle |= (uaddr &
> ~IOMMU_PAGE_MASK(tbl));
> }
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