drm/gem-shmem: Test for existence of page in mmap fault handler

Not having a page pointer in the mmap fault handler is an error. Test
for this situation and return VM_FAULT_SIGBUS if so. Also replace several
lookups of the page with a local variable.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patch.msgid.link/20260227114509.165572-3-tzimmermann@suse.de

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 1e3bfbf0cb979629e832c4c8f813347a7d0f4736..cf53619460307d4f031bcd6b6e0faa3e58221bbb 100644 (file)
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -574,31 +574,31 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
 {
        struct vm_area_struct *vma = vmf->vma;
        struct drm_gem_object *obj = vma->vm_private_data;
+       struct drm_device *dev = obj->dev;
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
        loff_t num_pages = obj->size >> PAGE_SHIFT;
-       vm_fault_t ret;
+       vm_fault_t ret = VM_FAULT_SIGBUS;
        struct page **pages = shmem->pages;
-       pgoff_t page_offset;
+       pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; /* page offset within VMA */
+       struct page *page;
        unsigned long pfn;
 
-       /* Offset to faulty address in the VMA. */
-       page_offset = vmf->pgoff - vma->vm_pgoff;
-
        dma_resv_lock(obj->resv, NULL);
 
-       if (page_offset >= num_pages ||
-           drm_WARN_ON_ONCE(obj->dev, !shmem->pages) ||
-           shmem->madv < 0) {
-               ret = VM_FAULT_SIGBUS;
+       if (page_offset >= num_pages || drm_WARN_ON_ONCE(dev, !shmem->pages) ||
+           shmem->madv < 0)
+               goto out;
+
+       page = pages[page_offset];
+       if (drm_WARN_ON_ONCE(dev, !page))
                goto out;
-       }
 
-       if (drm_gem_shmem_try_map_pmd(vmf, vmf->address, pages[page_offset])) {
+       if (drm_gem_shmem_try_map_pmd(vmf, vmf->address, page)) {
                ret = VM_FAULT_NOPAGE;
                goto out;
        }
 
-       pfn = page_to_pfn(pages[page_offset]);
+       pfn = page_to_pfn(page);
        ret = vmf_insert_pfn(vma, vmf->address, pfn);
 
  out: