On Thu, 2026-09-17 at 20:22 -0700, Matthew Brost wrote: > On Wed, Sep 16, 2026 at 03:23:33PM +0530, Arvind Yadav wrote: > > xe_vm_free() is the drm_gpuvm vm_free callback. It hands the final > > teardown to vm_destroy_work_func() on a workqueue and returns. > > > > drm_gpuvm_free() drops its device reference immediately after the > > callback returns: > > > > gpuvm->ops->vm_free(gpuvm); > > drm_dev_put(drm); > > > > vm_destroy_work_func() then keeps using device state: > > xe_pm_runtime_put() > > for an LR mode VM, ttm_lru_bulk_move_fini() on xe->ttm, and the > > tile > > iteration. If the freed VM held the last device reference, the work > > runs > > against a released xe_device. > > > > Take a device reference in xe_vm_free() and drop it once > > vm_destroy_work_func() has finished using the device. > > > > Cc: Matthew Brost <[email protected]> > > This is a fix, IMO. Ideally, we should probably push the delayed- > destroy > semantics into gpuvm if they are really needed. I'm also questioning > whether the VM destroy worker is actually required. This dates back > to > the very early days of Xe, and I doubt we've ever revisited whether > it > is necessary. > > Let's follow up with one of the following: > - Introduce async destroy in gpuvm and have it own the > drm_dev_get/put. > - Drop delayed destroy entirely in Xe.
We need to keep in mind that the drm file keeps a reference on the Xe module. So once the last close() callback has executed, the module can typically be unloaded, causing execution UAF. It's therefore not really recommended to keep file-related structures around with a refcount after close. Device references however typically don't necessarily keep the module pinned. I had a series to fix this for xe only, (Got stalled) [1], but in general we should be careful about leaking that assumption into DRM code. [1] https://patchwork.freedesktop.org/series/163298/ Thanks, Thomas > > As a temporary fix that can be backported, this looks good to me, so > with a Fixes tag: > > Reviewed-by: Matthew Brost <[email protected]> > > > Cc: Thomas Hellström <[email protected]> > > Cc: Himal Prasad Ghimiray <[email protected]> > > Cc: Rodrigo Vivi <[email protected]> > > Assisted-by: Claude:claude-opus-4-8 > > Signed-off-by: Arvind Yadav <[email protected]> > > --- > > drivers/gpu/drm/xe/xe_vm.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/drivers/gpu/drm/xe/xe_vm.c > > b/drivers/gpu/drm/xe/xe_vm.c > > index efa5ff6cc823..264bdab75de2 100644 > > --- a/drivers/gpu/drm/xe/xe_vm.c > > +++ b/drivers/gpu/drm/xe/xe_vm.c > > @@ -2054,12 +2054,21 @@ static void vm_destroy_work_func(struct > > work_struct *w) > > xe_file_put(vm->xef); > > > > kfree(vm); > > + > > + drm_dev_put(&xe->drm); > > } > > > > static void xe_vm_free(struct drm_gpuvm *gpuvm) > > { > > struct xe_vm *vm = container_of(gpuvm, struct xe_vm, > > gpuvm); > > > > + /* > > + * drm_gpuvm drops its device reference as soon as this > > callback > > + * returns, but vm_destroy_work_func() still uses device > > state. Hold a > > + * reference across the deferred work. > > + */ > > + drm_dev_get(&vm->xe->drm); > > + > > /* To destroy the VM we need to be able to sleep */ > > queue_work(system_dfl_wq, &vm->destroy_work); > > } > > -- > > 2.43.0 > >
