This is a note to let you know that I've just added the patch titled
ntb: Force physically contiguous allocation of rx ring buffers
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ntb-force-physically-contiguous-allocation-of-rx-rin.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 0f24d13d4d614b5f8d79d888f6b25c2513773a10
Author: Dave Jiang <dave.jiang@xxxxxxxxx>
Date: Thu Sep 5 14:22:07 2024 -0700
ntb: Force physically contiguous allocation of rx ring buffers
[ 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@xxxxxxxxx>
Fixes: f5ff79fddf0e ("dma-mapping: remove CONFIG_DMA_REMAP")
Tested-by: Jerry Dai <jerry.dai@xxxxxxxxx>
Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
Signed-off-by: Jon Mason <jdmason@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index f9e7847a378e7..c84fadfc63c52 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;
}
