Hi Am 17.02.21 um 17:59 schrieb Neil Roberts:
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.
I just want to ask if this is how the mmap callbacks are supposed to work now?
I have a number of patches in here that convert several drivers to the GEM object's mmap callback. They might not be affected by the vm_pgoff bug, but I'd like to submit something that could work in the longer term.
Best regards Thomas
It looks like panfrost is using drm_gem_shmem_purge so this might fix a potential bug there. Signed-off-by: Neil Roberts <nroberts@xxxxxxxxxx> --- drivers/gpu/drm/drm_gem_shmem_helper.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 9825c378dfa6..4b14157f1962 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -526,11 +526,16 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf) struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj); loff_t num_pages = obj->size >> PAGE_SHIFT; struct page *page; + pgoff_t page_offset;- if (vmf->pgoff >= num_pages || WARN_ON_ONCE(!shmem->pages))+ /* We don't use vmf->pgoff since that has the fake offset */ + page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT; + + if (page_offset < 0 || page_offset >= num_pages || + WARN_ON_ONCE(!shmem->pages)) return VM_FAULT_SIGBUS;- page = shmem->pages[vmf->pgoff];+ page = shmem->pages[page_offset];return vmf_insert_page(vma, vmf->address, page);} @@ -581,9 +586,6 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) 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);
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer
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