get_sg_table() merges physically contiguous pages without accounting
for the mapping device's maximum segment size. This affects both
importer mappings and the udmabuf misc device mapping used for CPU
access.
With DMA_API_DEBUG enabled, DMA_BUF_IOCTL_SYNC on a 64 MiB udmabuf
reports:
DMA-API: misc udmabuf: mapping sg segment longer than device claims to
support [len=65884160] [max=65536]
Use sg_alloc_table_from_pages_segment() with the mapping device's
maximum segment size. Keep a PAGE_SIZE minimum because the allocator
warns and returns -EINVAL for smaller limits.
Before commit 5bf888673e0d ("udmabuf: Do not create malformed
scatterlists"), each entry covered one page.
Fixes: 5bf888673e0d ("udmabuf: Do not create malformed scatterlists")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <[email protected]>
---
Notes:
Tested on v7.3-rc4-70-gfe2ec83746e5 in QEMU (x86_64, TCG) with
DMA_API_DEBUG (all_errors=1) and DMABUF_DEBUG, A/B against the same
base:
before after
DMA_BUF_IOCTL_SYNC, 64 MiB udmabuf 1 report 0
vivid import, 4 MiB udmabuf 2 reports 0
vivid import, 2 MiB hugetlb udmabuf 2 reports 0
frames captured 5/5 5/5
vb2-dma-contig rejected the non-contiguous import in both runs.
drivers/dma-buf/udmabuf.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index df6dd00462423..09f1eb8432f19 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -139,9 +139,13 @@ static struct sg_table *get_sg_table(struct device *dev,
struct dma_buf *buf,
if (!sg)
return ERR_PTR(-ENOMEM);
- ret = sg_alloc_table_from_pages(sg, ubuf->pages, ubuf->pagecount, 0,
- ubuf->pagecount << PAGE_SHIFT,
- GFP_KERNEL);
+ /* The SG allocator requires a segment limit of at least PAGE_SIZE. */
+ ret = sg_alloc_table_from_pages_segment(sg, ubuf->pages,
ubuf->pagecount,
+ 0, ubuf->pagecount <<
PAGE_SHIFT,
+ max_t(unsigned int,
+ dma_get_max_seg_size(dev),
+ PAGE_SIZE),
+ GFP_KERNEL);
if (ret < 0)
goto err_alloc;
--
2.53.0
