Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider: - [Critical] drm/msm: __do_map() uses sg_dma_address() as CPU physical address - [High] drm/msm: double dma_map_sgtable() and unmap in get_pages() and put_pages() - [High] drm/msm: NULL deref in get_pages() via drm_prime_gem_destroy() on error - [High] drm/msm: missing IOTLB invalidation in __unmap_iommu() and msm_iommu_map() --
commit e639a62aaac331070fa9f9ceece15e985cb308ad Author: Rob Clark <[email protected]> drm/msm: Convert map helper to use dma-address This series updates the MSM DRM driver to DMA-map GEM scatter-gather tables and converts the IOMMU and page table mapping helpers to iterate over DMA addresses and lengths rather than struct page pointers. > diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c > index 130ae27ee00be..72e3cd8bb1e7c 100644 > --- a/drivers/gpu/drm/msm/msm_gem.c > +++ b/drivers/gpu/drm/msm/msm_gem.c > @@ -190,6 +190,7 @@ static void update_lru(struct drm_gem_object *obj) > static struct page **get_pages(struct drm_gem_object *obj) > { > struct msm_gem_object *msm_obj = to_msm_bo(obj); > + int ret = 0; > > msm_gem_assert_locked(obj); > > @@ -209,19 +210,26 @@ static struct page **get_pages(struct drm_gem_object > *obj) > return p; > } > > - update_device_mem(dev->dev_private, obj->size); > - > msm_obj->pages = p; > > msm_obj->sgt = drm_prime_pages_to_sg(obj->dev, p, npages); > if (IS_ERR(msm_obj->sgt)) { > - void *ptr = ERR_CAST(msm_obj->sgt); > - > DRM_DEV_ERROR(dev->dev, "failed to allocate sgt\n"); > - msm_obj->sgt = NULL; > - return ptr; > + ret = PTR_ERR(msm_obj->sgt); > + goto error; > } > > + ret = dma_map_sgtable(drm_dev_dma_dev(obj->dev), > + msm_obj->sgt, > + DMA_BIDIRECTIONAL, > + DMA_ATTR_SKIP_CPU_SYNC); > + if (ret) { > + DRM_DEV_ERROR(dev->dev, "could not map sgtable: %d\n", > ret); > + goto error; > + } > + > + update_device_mem(dev->dev_private, obj->size); > + > /* For non-cached buffers, ensure the new pages are clean > * because display controller, GPU, etc. are not coherent: > */ > @@ -232,6 +240,16 @@ static struct page **get_pages(struct drm_gem_object > *obj) > } > > return msm_obj->pages; > + > +error: > + if (!IS_ERR(msm_obj->sgt)) > + drm_prime_gem_destroy(obj, msm_obj->sgt); [Severity: High] Won't calling drm_prime_gem_destroy() in the error path of get_pages() cause a NULL pointer dereference when dma_map_sgtable() fails? In drivers/gpu/drm/msm/msm_gem.c, get_pages() is only used for non-imported GEM objects and rejects imported objects at the start: if (drm_WARN_ON_ONCE(obj->dev, drm_gem_is_imported(obj))) return ERR_PTR(-EINVAL); Because obj->import_attach is NULL for native GEM objects, jumping to error after drm_prime_pages_to_sg() succeeds calls drm_prime_gem_destroy(), which dereferences attach->dmabuf: attach = obj->import_attach; if (sg) dma_buf_unmap_attachment_unlocked(attach, sg, DMA_BIDIRECTIONAL); dma_buf = attach->dmabuf; Should this error path call sg_free_table(msm_obj->sgt) and kfree(msm_obj->sgt) instead of drm_prime_gem_destroy()? > + msm_obj->sgt = NULL; > + > + drm_gem_put_pages(obj, msm_obj->pages, false, false); > + msm_obj->pages = NULL; > + > + return ERR_PTR(ret); > } > > static void put_pages(struct drm_gem_object *obj) > @@ -246,18 +264,21 @@ static void put_pages(struct drm_gem_object *obj) > drm_gpuvm_bo_gem_evict(obj, true); > > if (msm_obj->pages) { > - if (msm_obj->sgt) { > - /* For non-cached buffers, ensure the new > - * pages are clean because display controller, > - * GPU, etc. are not coherent: > - */ > - if (msm_obj->flags & MSM_BO_WC) > - sync_for_cpu(msm_obj); > + /* For non-cached buffers, ensure the new > + * pages are clean because display controller, > + * GPU, etc. are not coherent: > + */ > + if (msm_obj->flags & MSM_BO_WC) > + sync_for_cpu(msm_obj); > > - sg_free_table(msm_obj->sgt); > - kfree(msm_obj->sgt); > - msm_obj->sgt = NULL; > - } > + dma_unmap_sgtable(drm_dev_dma_dev(obj->dev), > + msm_obj->sgt, > + DMA_BIDIRECTIONAL, > + DMA_ATTR_SKIP_CPU_SYNC); [Severity: High] Doesn't this map msm_obj->sgt twice in get_pages() and unmap it twice in put_pages() whenever MSM_BO_WC is set? In get_pages(), dma_map_sgtable() is called with DMA_ATTR_SKIP_CPU_SYNC, and then if (msm_obj->flags & MSM_BO_WC) is true, sync_for_device() is called: static void sync_for_device(struct msm_gem_object *msm_obj) { struct device *dev = msm_obj->base.dev->dev; dma_map_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0); } Symmetrically, in put_pages(), sync_for_cpu() calls dma_unmap_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0), followed immediately by a second dma_unmap_sgtable() with DMA_ATTR_SKIP_CPU_SYNC on the same sg_table and device. With CONFIG_DMA_API_DEBUG enabled, mapping an already-mapped scatterlist triggers overlapping DMA-API debug warnings in debug_dma_map_sg() and double-unmap warnings in debug_dma_unmap_sg(). Additionally, if use_dma_iommu(dev) is true, the second dma_map_sgtable() overwrites sg_dma_address(sg) and leaks the first IOVA range in group->default_domain, while the second dma_unmap_sgtable() frees the second IOVA range twice in iommu_dma_unmap_sg(). > diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c > index da6782fca6bd2..6258c942e66ad 100644 > --- a/drivers/gpu/drm/msm/msm_iommu.c > +++ b/drivers/gpu/drm/msm/msm_iommu.c [ ... ] > @@ -135,6 +137,83 @@ static int msm_iommu_pagetable_unmap(struct msm_mmu > *mmu, u64 iova, size_t size) > size -= unmapped; > } > > + return ret; > +} > + > +static inline int > +__do_map(unsigned long pgsize_bitmap, u64 iova, struct sg_table *sgt, size_t > off, > + size_t len, int prot, void *arg, map_fn map, unmap_fn unmap) > +{ > + struct scatterlist *sg; > + u64 addr = iova; > + unsigned int i; > + > + for_each_sgtable_dma_sg (sgt, sg, i) { > + size_t size = sg_dma_len(sg); > + phys_addr_t phys = sg_dma_address(sg); [Severity: Critical] Is it safe to treat sg_dma_address(sg) and sg_dma_len(sg) as CPU physical addresses and physical segment lengths when programming the GPU and display page tables in __do_map()? Both __map_pgtable() (calling io_pgtable_ops->map_pages()) and __map_iommu() (calling iommu_domain->ops->map_pages()) expect paddr to be a CPU physical address. In get_pages() and drm_gem_prime_import(), the sg_table is DMA-mapped for drm_dev_dma_dev(obj->dev) (which is obj->dev->dev). As noted in the comment above sync_for_device() in drivers/gpu/drm/msm/msm_gem.c and in msm_kms_init_vm() in drivers/gpu/drm/msm/msm_kms.c, depending on the display generation, the display IOMMU is wired either to the parent mdss device or directly to the mdp sub-node (obj->dev->dev): if (device_iommu_mapped(mdp_dev)) iommu_dev = mdp_dev; else if (mdss_dev && device_iommu_mapped(mdss_dev)) iommu_dev = mdss_dev; On platforms where the IOMMU is wired to the mdp node and the IOMMU driver does not select IOMMU_DOMAIN_IDENTITY as the default domain (such as SDM630 / SDM660 with "qcom,mdp5", MSM8996, and platforms using qcom_iommu), the IOMMU core allocates a DMA default_domain during probe and calls iommu_setup_dma_ops(), setting use_dma_iommu(dev) to true. Even when msm_iommu_new() later attaches an unmanaged domain via iommu_attach_device(), use_dma_iommu(dev) remains true. In kernel/dma/mapping.c, dma_go_direct() checks use_dma_iommu(dev) before !ops: static bool dma_go_direct(struct device *dev, dma_addr_t mask, const struct dma_map_ops *ops) { if (use_dma_iommu(dev)) return false; if (likely(!ops)) return true; As a result, dma_map_sgtable() calls iommu_dma_map_sg(), which allocates a virtual IOVA in group->default_domain, coalesces physically non-contiguous segments into contiguous IOVA ranges, and writes that virtual IOVA into sg_dma_address(sg) and the coalesced length into sg_dma_len(sg). Passing those values to __do_map() will program the GPU and display page tables with virtual IOVAs instead of physical addresses. [ ... ] > @@ -684,12 +731,27 @@ static void msm_iommu_detach(struct msm_mmu *mmu) > iommu_detach_device(iommu->domain, mmu->dev); > } > > +static size_t > +__unmap_iommu(void *arg, u64 iova, size_t pgsize, size_t pgcount) > +{ > + struct iommu_domain *domain = arg; > + return domain->ops->unmap_pages(domain, iova, pgsize, pgcount, NULL); > +} > + > +static int > +__map_iommu(void *arg, phys_addr_t paddr, u64 iova, size_t pgsize, > + size_t pgcount, int prot, size_t *mapped) > +{ > + struct iommu_domain *domain = arg; > + return domain->ops->map_pages(domain, iova, paddr, pgsize, pgcount, > + prot, GFP_KERNEL, mapped); > +} > + > static int msm_iommu_map(struct msm_mmu *mmu, uint64_t iova, > struct sg_table *sgt, size_t off, size_t len, > int prot) > { > - struct msm_iommu *iommu = to_msm_iommu(mmu); > - ssize_t ret; > + struct iommu_domain *domain = to_msm_iommu(mmu)->domain; > > WARN_ON(off != 0); > > @@ -697,23 +759,23 @@ static int msm_iommu_map(struct msm_mmu *mmu, uint64_t > iova, > if (iova & BIT_ULL(48)) > iova |= GENMASK_ULL(63, 49); > > - ret = iommu_map_sgtable(iommu->domain, iova, sgt, prot); > - if (ret < 0) > - return ret; > - > - return (ret == len) ? 0 : -EINVAL; > + return __do_map(domain->pgsize_bitmap, iova, sgt, off, len, prot, > + domain, __map_iommu, __unmap_iommu); > } > > static int msm_iommu_unmap(struct msm_mmu *mmu, uint64_t iova, size_t len) > { > - struct msm_iommu *iommu = to_msm_iommu(mmu); > + struct iommu_domain *domain = to_msm_iommu(mmu)->domain; > + int ret; > > if (iova & BIT_ULL(48)) > iova |= GENMASK_ULL(63, 49); > > - iommu_unmap(iommu->domain, iova, len); > + ret = __do_unmap(domain->pgsize_bitmap, iova, len, domain, > __unmap_iommu); > > - return 0; > + iommu_flush_iotlb_all(domain); > + > + return ret; > } [Severity: High] Can replacing iommu_map_sgtable() and iommu_unmap() with __do_map() and __do_unmap() leave stale IOTLB entries behind? There appear to be three cases where IOTLB maintenance is skipped: 1. In msm_iommu_map(), if __do_map() fails after mapping some pages, it rolls back the partial mapping via __do_unmap(..., __unmap_iommu). Unlike msm_iommu_pagetable_map(), msm_iommu_map() does not call iommu_flush_iotlb_all(domain) on error. 2. In __unmap_iommu(), NULL is passed for the struct iommu_iotlb_gather pointer to domain->ops->unmap_pages(). In drivers/iommu/io-pgtable-arm.c, __arm_lpae_unmap() only calls io_pgtable_tlb_add_page() when gather is non-NULL: if (gather && !iommu_iotlb_gather_queued(gather)) io_pgtable_tlb_add_page(data, gather, iova, size); On SoCs using drivers/iommu/arm/arm-smmu/qcom_iommu.c, qcom_iommu_flush_iotlb_all() only issues ARM_SMMU_CB_TLBSYNC via qcom_iommu_tlb_sync() and relies on qcom_iommu_tlb_add_page() issuing ARM_SMMU_CB_S1_TLBIVAL during unmap_pages(). Passing gather as NULL skips the TLB invalidation commands altogether. 3. On APQ8064 (drivers/iommu/msm_iommu.c), msm_iommu_ops implements .iotlb_sync_map = msm_iommu_sync_map while leaving .flush_iotlb_all = NULL, so calling domain->ops->map_pages() directly in msm_iommu_map() bypasses the iotlb_sync_map callback that iommu_map_sgtable() previously invoked. -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=5
