[PATCH v2] drm/vgem: Restore mmap functionality

[Thomas Zimmermann]

Commit 375cca1cfeb5 ("drm/vgem: Implement mmap as GEM object function")
accidentally removed the actual mmap functionality from vgem. Restore
the original implementation by restoring the vm_pgoff in the mmap code.

Fixes access to unmapped memory:

[  106.591744] BUG: KASAN: vmalloc-out-of-bounds in do_fault+0x38/0x480
[  106.598154] Read of size 8 at addr ffffffffc10c44a8 by task vgem_basic/1514
[  106.605173]
[  106.606678] CPU: 1 PID: 1514 Comm: vgem_basic Tainted: G            E     5.13.0-1-default+ #990
[  106.615535] Hardware name: Dell Inc. OptiPlex 9020/0N4YC8, BIOS A24 10/24/2018
[  106.622818] Call Trace:
[  106.625289]  dump_stack+0xa5/0xdc
[  106.628642]  print_address_description.constprop.0+0x18/0x100
[  106.634439]  ? do_fault+0x38/0x480
[  106.637872]  kasan_report.cold+0x7c/0xd8
[  106.641834]  ? do_fault+0x38/0x480
[  106.645274]  do_fault+0x38/0x480
[  106.648535]  __handle_mm_fault+0x935/0xb00
[  106.652676]  ? vm_iomap_memory+0xe0/0xe0
[  106.656634]  ? __lock_release+0x12f/0x4e0
[  106.660696]  ? count_memcg_event_mm.part.0+0xb9/0x190
[  106.665799]  handle_mm_fault+0xd0/0x370
[  106.669675]  do_user_addr_fault+0x2a0/0x8c0
[  106.673908]  exc_page_fault+0x64/0xf0
[  106.677604]  ? asm_exc_page_fault+0x8/0x30
[  106.681739]  asm_exc_page_fault+0x1e/0x30
[  106.685782] RIP: 0033:0x402e12
...

v2:
	* restore vma.vm_pgoff instead of mapping the pages

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Fixes: 375cca1cfeb5 ("drm/vgem: Implement mmap as GEM object function")
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: Christian König <christian.koenig at amd.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: "Christian König" <christian.koenig at amd.com>
Cc: Melissa Wen <melissa.srw at gmail.com>
Cc: Jason Gunthorpe <jgg at ziepe.ca>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Lee Jones <lee.jones at linaro.org>
---
 drivers/gpu/drm/vgem/vgem_drv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
index df634aa52638..e92d1f2e02c4 100644
--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -364,8 +364,8 @@ static void vgem_prime_vunmap(struct drm_gem_object *obj, struct dma_buf_map *ma
 
 static int vgem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
 {
-	vma_set_file(vma, obj->filp);
-	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
+	vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node);
+	vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
 	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 
-- 
2.32.0