6.1-stable review patch. If anyone has any objections, please let me know.
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From: Dave Jiang dave.jiang@intel.com
[ Upstream commit 061a785a114f159e990ea8ed8d1b7dca4b41120f ]
Physical addresses under IOVA on x86 platform are mapped contiguously as a side effect before the patch that removed CONFIG_DMA_REMAP. The NTB rx buffer ring is a single chunk DMA buffer that is allocated against the NTB PCI device. If the receive side is using a DMA device, then the buffers are remapped against the DMA device before being submitted via the dmaengine API. This scheme becomes a problem when the physical memory is discontiguous. When dma_map_page() is called on the kernel virtual address from the dma_alloc_coherent() call, the new IOVA mapping no longer points to all the physical memory allocated due to being discontiguous. Change dma_alloc_coherent() to dma_alloc_attrs() in order to force DMA_ATTR_FORCE_CONTIGUOUS attribute. This is the best fix for the circumstance. A potential future solution may be having the DMA mapping API providing a way to alias an existing IOVA mapping to a new device perhaps.
This fix is not to fix the patch pointed to by the fixes tag, but to fix the issue arised in the ntb_transport driver on x86 platforms after the said patch is applied.
Reported-by: Jerry Dai jerry.dai@intel.com Fixes: f5ff79fddf0e ("dma-mapping: remove CONFIG_DMA_REMAP") Tested-by: Jerry Dai jerry.dai@intel.com Signed-off-by: Dave Jiang dave.jiang@intel.com Signed-off-by: Jon Mason jdmason@kudzu.us Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/ntb/ntb_transport.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c index 9532108d2dce1..5b25260e59253 100644 --- a/drivers/ntb/ntb_transport.c +++ b/drivers/ntb/ntb_transport.c @@ -807,16 +807,29 @@ static void ntb_free_mw(struct ntb_transport_ctx *nt, int num_mw) }
static int ntb_alloc_mw_buffer(struct ntb_transport_mw *mw, - struct device *dma_dev, size_t align) + struct device *ntb_dev, size_t align) { dma_addr_t dma_addr; void *alloc_addr, *virt_addr; int rc;
- alloc_addr = dma_alloc_coherent(dma_dev, mw->alloc_size, - &dma_addr, GFP_KERNEL); + /* + * The buffer here is allocated against the NTB device. The reason to + * use dma_alloc_*() call is to allocate a large IOVA contiguous buffer + * backing the NTB BAR for the remote host to write to. During receive + * processing, the data is being copied out of the receive buffer to + * the kernel skbuff. When a DMA device is being used, dma_map_page() + * is called on the kvaddr of the receive buffer (from dma_alloc_*()) + * and remapped against the DMA device. It appears to be a double + * DMA mapping of buffers, but first is mapped to the NTB device and + * second is to the DMA device. DMA_ATTR_FORCE_CONTIGUOUS is necessary + * in order for the later dma_map_page() to not fail. + */ + alloc_addr = dma_alloc_attrs(ntb_dev, mw->alloc_size, + &dma_addr, GFP_KERNEL, + DMA_ATTR_FORCE_CONTIGUOUS); if (!alloc_addr) { - dev_err(dma_dev, "Unable to alloc MW buff of size %zu\n", + dev_err(ntb_dev, "Unable to alloc MW buff of size %zu\n", mw->alloc_size); return -ENOMEM; } @@ -845,7 +858,7 @@ static int ntb_alloc_mw_buffer(struct ntb_transport_mw *mw, return 0;
err: - dma_free_coherent(dma_dev, mw->alloc_size, alloc_addr, dma_addr); + dma_free_coherent(ntb_dev, mw->alloc_size, alloc_addr, dma_addr);
return rc; }