On Fri, Sep 25, 2026 at 7:20 PM Jianfeng Liu <[email protected]> wrote: > > This reverts commit 143755bdabaa96776c24f878014608e9cb44f930. > > That commit fixed a dangling reference in the DMABUF_DEBUG default > and thereby enabled the option - and with it the page-stripping > sg_table wrapper that dma_buf_map_attachment() hands to importers - > on every kernel with DEBUG_KERNEL=y, i.e. virtually every distro > kernel. > > drm/msm is broken by the wrapper. Both of msm's map paths consume > sg->length and sg_phys() of the attachment sg_table: > msm_iommu_pagetable_map() for the per-process GPU pagetables, and > iommu_map_sg() (via iommu_map_sgtable()) for scanout. The wrapper > zeroes sg->length and strips the page pointers, so mappings of > imported dma-bufs silently map nothing, and userspace observes > arm-smmu translation faults from UCHE, e.g. during hardware video > decode (clapper, chromium) on Adreno systems: > > gpu fault: ttbr0=000000088a889000 iova=000000010741c000 dir=READ > type=TRANSLATION source=UCHE > > Bisected on a Snapdragon X1E78100 laptop as v7.3-rc3 good, > v7.3-rc4 bad, culprit 143755bdabaa9. > > Switching msm to sg_dma_address()/sg_dma_len() is not a trivial fix > either: those fields are only valid for sg_tables that msm has > dma-mapped itself, which native non-MSM_BO_WC objects' sg_tables > are not, so the conversion needs more work. The msm maintainer has > therefore requested restoring the previous default for v7.3, to be > revisited once msm no longer consumes struct page and sg->length of > imported sg_tables.
I sent a series[1] to remove the remaining (direct) use of pages for imported dma-bufs, and remove use of drm_prime_sg_to_page_array() (so one less caller of the deprecated function). This on its own won't solve the problems with CONFIG_DMABUF_DEBUG. There is still the indirect dependency on pages when mapping sgt's. I won't have time to work on that until after XDC, so it won't be a v7.3 thing, and _probably_ won't be a v7.4 thing at this point. But hopefully I can come up with something for v7.5. Until then, please apply this revert. BR, -R [1] https://patchwork.freedesktop.org/series/175045/ > Link: > https://lore.kernel.org/linux-arm-msm/[email protected]/ > Suggested-by: Rob Clark <[email protected]> > Cc: Christian König <[email protected]> > Cc: Sumit Semwal <[email protected]> > Cc: Karl Mehltretter <[email protected]> > > Signed-off-by: Jianfeng Liu <[email protected]> > --- > > drivers/dma-buf/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig > index e4f078a326a41..7efc0f0d07126 100644 > --- a/drivers/dma-buf/Kconfig > +++ b/drivers/dma-buf/Kconfig > @@ -43,7 +43,7 @@ config UDMABUF > config DMABUF_DEBUG > bool "DMA-BUF debug checks" > depends on DMA_SHARED_BUFFER > - default y if DEBUG_KERNEL > + default y if DEBUG > help > This option enables additional checks for DMA-BUF importers and > exporters. Specifically it validates that importers do not peek at > the > --- > base-commit: 93f51579e7df248780214094418f205253383cc5 > branch: revert-dmabuf-debug-for-7.3 > > -- > 2.47.3 >
