On 9/1/26 19:08, David Hu wrote:
> From: David Hu <xuehaohu(a)google.com>
>
> This series address two related issues in scatter-gather mapping,
> specifically for the MMIO based dma-buf mapping. The fixes ensure
> sgt mapping is correct, and proper for large MMIO regions.
>
> Patch 1 fixes a silent integer overflow for mapping length exceeding 4G
> (Previously submitted as [PATCH v7] dma-buf: Fix silent overflow for
> phys vec to sgt)
> https://lore.kernel.org/all/20260609164047.486227-1-xuehaohu@google.com/
>
> Patch 2 Splits sgl by largest page aligned chunk
> (Previously submitted as [PATCH v3] dma-buf: Split sgl by largest page-aligned chunk)
> https://lore.kernel.org/all/20260722233806.3922093-1-dhu@x6u.co/
*sigh* such issues are exactly the reason why I didn't wanted the dma-mapping stuff inside DMA-buf. That clearly doesn't belong here.
I'm going to push those fixes to drm-misc-next now, but when there are more issues like that will mark the code as abandoned and not maintained.
Regards,
Christian.
>
> Changes in v8:
> - Combined the two patches into one unified series to avoid merge
> conflicts.
> - Collected Reviewed-by tag from Leon Romanovsky for Patch 2.
>
> David Hu (2):
> dma-buf: Fix silent overflow for phys vec to sgt
> dma-buf: Split sgl by largest page-aligned chunk
>
> drivers/dma-buf/dma-buf-mapping.c | 31 +++++++++++++++++++++----------
> 1 file changed, 21 insertions(+), 10 deletions(-)
>
> --
> 2.55.0.897.gb25b4bd76c-goog
>
Applied this to drm-misc-fixes.
On 8/19/26 15:44, Taimuraz Kaitmazov wrote:
> SYNC_BO clflushes an imported BO's scatterlist. An importer may not do
> that: the memory belongs to the exporter, and dma-buf gives the importer
> no interface to ask for maintenance on it. Refuse the request instead.
>
> is_import_bo() is (obj)->attach, which covers more than foreign buffers.
> A userptr BO arrives through a ubuf, and on a carveout device every share
> BO and the device heap arrive through a cbuf, so SYNC_BO answers
> -EOPNOTSUPP for those too, including the AMDXDNA_BO_DEV path that flushes
> through its heap.
>
> Only the ubuf case gives up maintenance it was getting: on a 64 MiB
> userptr BO a 4 KiB sync and a full sync both cost 659 us, this arm having
> ignored the range. amdxdna_cbuf_map() fills in only the DMA address and
> length, so drm_clflush_sg() already walks zero pages on carveout memory.
> Userspace maintains these through the mapping it already holds, as XRT's
> buffer::sync() does unless it is told to sync through the driver.
>
> Suggested-by: Lizhi Hou <lizhi.hou(a)amd.com>
> Signed-off-by: Taimuraz Kaitmazov <taimuraz(a)kaitmazov.com>
> Reviewed-by: Lizhi Hou <lizhi.hou(a)amd.com>
> ---
> drivers/accel/amdxdna/amdxdna_gem.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
> index 0e0f844526ca..4be5298d1062 100644
> --- a/drivers/accel/amdxdna/amdxdna_gem.c
> +++ b/drivers/accel/amdxdna/amdxdna_gem.c
> @@ -1224,6 +1224,9 @@ static int amdxdna_flush_bo(struct amdxdna_gem_obj *abo, u64 offset, u64 size)
> {
> u64 end;
>
> + if (is_import_bo(abo))
> + return -EOPNOTSUPP;
> +
> if (offset >= abo->mem.size)
> return -EINVAL;
>
> @@ -1234,9 +1237,7 @@ static int amdxdna_flush_bo(struct amdxdna_gem_obj *abo, u64 offset, u64 size)
> if (!size)
> return 0;
>
> - if (is_import_bo(abo))
> - drm_clflush_sg(abo->base.sgt);
> - else if (amdxdna_gem_vmap(abo))
> + if (amdxdna_gem_vmap(abo))
> drm_clflush_virt_range(amdxdna_gem_vmap(abo) + offset, size);
> else if (abo->base.pages)
> drm_clflush_pages(abo->base.pages, abo->mem.size >> PAGE_SHIFT);
On Tue, Sep 01, 2026 at 05:08:49PM +0000, David Hu wrote:
> From: David Hu <xuehaohu(a)google.com>
>
> Currently, `fill_sg_entry()` splits the scatterlist using `UINT_MAX`.
> This creates a non-page-aligned DMA length (`0xFFFFFFFF`) for the
> first entry, resulting in non-page-aligned DMA addresses for all
> subsequent entries.
This patch is fine, but pedenatically a scatterlist's entry limit
should be bounded to dma_get_max_seg_size(), though I don't think it
helps this. Operating scatterlists at the size limits has proven
problematic in a number of places already...
> In addition, a non-page-aligned sgl length will trigger an edge case
> in `ib_umem_find_best_pgsz()`. In case of a discontinuity in later
> buffers, we will have a `va` with lowest bit set to 1. That will lead
> to `ib_umem_find_best_pgsz()` always return 0, and break the promise
> to find best page size for the mapping on the NIC side.
That's an IB side bug, the newer logic that joins adjacent SGLs should
have avoided it?
Jason
