From: Greg Kroah-Hartman gregkh@linuxfoundation.org
From: Neil Roberts nroberts@igalia.com
commit 11d5a4745e00e73745774671dbf2fb07bd6e2363 upstream.
When mmapping the shmem, it would previously adjust the pgoff in the vm_area_struct to remove the fake offset that is added to be able to identify the buffer. This patch removes the adjustment and makes the fault handler use the vm_fault address to calculate the page offset instead. Although using this address is apparently discouraged, several DRM drivers seem to be doing it anyway.
The problem with removing the pgoff is that it prevents drm_vma_node_unmap from working because that searches the mapping tree by address. That doesn't work because all of the mappings are at offset 0. drm_vma_node_unmap is being used by the shmem helpers when purging the buffer.
This fixes a bug in Panfrost which is using drm_gem_shmem_purge. Without this the mapping for the purged buffer can still be accessed which might mean it would access random pages from other buffers
v2: Don't check whether the unsigned page_offset is less than 0.
Cc: stable@vger.kernel.org Fixes: 17acb9f35ed7 ("drm/shmem: Add madvise state and purge helpers") Signed-off-by: Neil Roberts nroberts@igalia.com Reviewed-by: Steven Price steven.price@arm.com Signed-off-by: Steven Price steven.price@arm.com Link: https://patchwork.freedesktop.org/patch/msgid/20210223155125.199577-3-nrober... Signed-off-by: Maarten Lankhorst maarten.lankhorst@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/drm_gem_shmem_helper.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -527,15 +527,19 @@ static vm_fault_t drm_gem_shmem_fault(st loff_t num_pages = obj->size >> PAGE_SHIFT; vm_fault_t ret; struct page *page; + pgoff_t page_offset; + + /* We don't use vmf->pgoff since that has the fake offset */ + page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
mutex_lock(&shmem->pages_lock);
- if (vmf->pgoff >= num_pages || + if (page_offset >= num_pages || WARN_ON_ONCE(!shmem->pages) || shmem->madv < 0) { ret = VM_FAULT_SIGBUS; } else { - page = shmem->pages[vmf->pgoff]; + page = shmem->pages[page_offset];
ret = vmf_insert_page(vma, vmf->address, page); } @@ -591,9 +595,6 @@ int drm_gem_shmem_mmap(struct drm_gem_ob struct drm_gem_shmem_object *shmem; int ret;
- /* Remove the fake offset */ - vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node); - if (obj->import_attach) { /* Drop the reference drm_gem_mmap_obj() acquired.*/ drm_gem_object_put(obj);