Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues: - [Critical] The VMA reference count (`vma_ref`) is decremented and checked outside of the VMA/object lock, leading to a TOCTOU race where an active VMA can be unmapped and freed while in use by another thread. -- --- Patch [1]: [PATCH 1/2] drm/msm: factor out a locking put_iova_spaces() wrapper --- commit 3d4e26e168daef686a19b61570238be2722c0b4d Author: Dmitry Baryshkov <[email protected]> Subject: drm/msm: factor out a locking put_iova_spaces() wrapper This commit factors out a locking put_iova_spaces_locked() wrapper and updates callers. It aims to clean up redundant lock, tear down, and unlock sequences around the teardown path. > diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c > index de4e60e28a711..8b979d84bb958 100644 > --- a/drivers/gpu/drm/msm/msm_gem.c > +++ b/drivers/gpu/drm/msm/msm_gem.c [ ... ] > @@ -105,11 +113,7 @@ void msm_gem_vma_put(struct drm_gem_object *obj) > return; > > #ifdef CONFIG_DRM_MSM_KMS > - struct drm_exec exec; > - > - msm_gem_lock_vm_and_obj(&exec, obj, priv->kms->vm); > put_iova_spaces(obj, priv->kms->vm, true, "vma_put"); > - drm_exec_fini(&exec); /* drop locks */ > #endif > } [ ... ] > @@ -408,8 +412,8 @@ static struct drm_gpuva *lookup_vma(struct drm_gem_object > *obj, > * mapping. > */ > static void > -put_iova_spaces(struct drm_gem_object *obj, struct drm_gpuvm *vm, > - bool close, const char *reason) > +put_iova_spaces_locked(struct drm_gem_object *obj, struct drm_gpuvm *vm, > + bool close, const char *reason) > { > struct drm_gpuvm_bo *vm_bo, *tmp; [Severity: Critical] This is a pre-existing issue, but can the lockless decrement of vma_ref in msm_gem_vma_put() cause a race condition? If CPU1 calls msm_gem_close() -> msm_gem_vma_put() and decrements vma_ref to 0, but gets preempted before taking the lock and calling put_iova_spaces(): CPU2 could concurrently open the GEM object (e.g., via flink), calling msm_gem_open() -> msm_gem_vma_get(), incrementing vma_ref back to 1, mapping the object, and submitting a job. When CPU1 resumes, it continues into put_iova_spaces() and eventually put_iova_spaces_locked(): drivers/gpu/drm/msm/msm_gem.c:put_iova_spaces_locked() { ... drm_gpuvm_bo_for_each_va_safe (vma, vmatmp, vm_bo) { msm_gem_vma_unmap(vma, reason); if (close) msm_gem_vma_close(vma); } ... } Since vma_ref isn't re-checked inside the lock, the IOVA space is torn down unconditionally. Could this result in tearing down an active IOVA mapping while the GPU is executing a job, leading to an IOMMU fault or memory corruption? -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
