[PATCH] drm/xen: Add missing VM_DONTEXPAND flag in mmap callback

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

With Xen PV Display driver in use the "expected" VM_DONTEXPAND flag
is not set (neither explicitly nor implicitly), so the driver hits
the code path in drm_gem_mmap_obj() which triggers the WARNING.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
---
This patch eliminates a WARNING which occurs during running any user space
application over drm (weston, modetest, etc) using PV Display frontend
in Xen guest (it worth mentioning the frontend still works despite the WARNING):

root@salvator-x-h3-4x2g-xt-domu:~# modetest -M xendrm-du -s 31:1920x1080
(XEN) common/grant_table.c:1882:d2v0 Expanding d2 grant table from 5 to 9 frames
[   31.566759] ------------[ cut here ]------------
[   31.566811] WARNING: CPU: 0 PID: 235 at drivers/gpu/drm/drm_gem.c:1055 
drm_gem_mmap_obj+0x16c/0x180
[   31.566864] Modules linked in:
[   31.566886] CPU: 0 PID: 235 Comm: modetest Not tainted 
5.18.0-rc4-yocto-standard-00009-gabe87d78bbc9 #1
[   31.566922] Hardware name: XENVM-4.17 (DT)
[   31.566940] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   31.566973] pc : drm_gem_mmap_obj+0x16c/0x180
[   31.567001] lr : drm_gem_mmap_obj+0x78/0x180
[   31.567026] sp : ffff800009d03bb0
[   31.567044] x29: ffff800009d03bb0 x28: 0000000000000008 x27: ffff0001c42d43c0
[   31.567080] x26: ffff0001c42d4cc0 x25: 00000000000007e9 x24: ffff0001c0136000
[   31.567116] x23: ffff0001c0310000 x22: ffff0001c4002b80 x21: 0000000000000000
[   31.567150] x20: ffff0001c42d43c0 x19: ffff0001c0137600 x18: 0000000000000001
[   31.567186] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000035c81
[   31.567220] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
[   31.567258] x11: 0000000000100000 x10: 0000ffff95d69000 x9 : ffff0001c435ac30
[   31.567294] x8 : ffff8001f65ce000 x7 : 0000000000000001 x6 : ffff0001c24de000
[   31.567329] x5 : ffff800009d03a10 x4 : 0000000000000090 x3 : 0000000010046400
[   31.567365] x2 : 00000000000007e9 x1 : 9dd8cb7c02b1bd00 x0 : 00000000100000fb
[   31.567401] Call trace:
[   31.567415]  drm_gem_mmap_obj+0x16c/0x180
[   31.567439]  drm_gem_mmap+0x128/0x228
[   31.567460]  mmap_region+0x384/0x5a0
[   31.567484]  do_mmap+0x354/0x4f0
[   31.567505]  vm_mmap_pgoff+0xdc/0x108
[   31.567529]  ksys_mmap_pgoff+0x1b8/0x208
[   31.567550]  __arm64_sys_mmap+0x30/0x48
[   31.567576]  invoke_syscall+0x44/0x108
[   31.567599]  el0_svc_common.constprop.0+0xcc/0xf0
[   31.567629]  do_el0_svc+0x24/0x88
[   31.567649]  el0_svc+0x2c/0x88
[   31.567686]  el0t_64_sync_handler+0xb0/0xb8
[   31.567708]  el0t_64_sync+0x18c/0x190
[   31.567731] ---[ end trace 0000000000000000 ]---
setting mode 1920x1080-60.00Hz@XR24 on connectors 31, crtc 34
---
 drivers/gpu/drm/xen/xen_drm_front_gem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c 
b/drivers/gpu/drm/xen/xen_drm_front_gem.c
index 5a5bf4e..e31554d 100644
--- a/drivers/gpu/drm/xen/xen_drm_front_gem.c
+++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c
@@ -71,7 +71,7 @@ static int xen_drm_front_gem_object_mmap(struct 
drm_gem_object *gem_obj,
         * the whole buffer.
         */
        vma->vm_flags &= ~VM_PFNMAP;
-       vma->vm_flags |= VM_MIXEDMAP;
+       vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;
        vma->vm_pgoff = 0;
 
        /*
-- 
2.7.4