drm/msm: Add a way for userspace to allocate GPU iova

The motivation at this point is mainly native userspace mesa driver in a
VM guest.  The one remaining synchronous "hotpath" is buffer allocation,
because guest needs to wait to know the bo's iova before it can start
emitting cmdstream/state that references the new bo.  By allocating the
iova in the guest userspace, we no longer need to wait for a response
from the host, but can just rely on the allocation request being
processed before the cmdstream submission.  Allocation failures (OoM,
etc) would just be treated as context-lost (ie. GL_GUILTY_CONTEXT_RESET)
or subsequent allocations (or readpix, etc) can raise GL_OUT_OF_MEMORY.

v2: Fix inuse check
v3: Change mismatched iova case to -EBUSY

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://lore.kernel.org/r/20220411215849.297838-11-robdclark@gmail.com
Signed-off-by: Rob Clark <robdclark@chromium.org>

1 files changed, 48 insertions, 0 deletions

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 21986c321458..52fe6428a341 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -525,6 +525,54 @@ int msm_gem_get_iova(struct drm_gem_object *obj,
 	return ret;
 }
 
+static int clear_iova(struct drm_gem_object *obj,
+		      struct msm_gem_address_space *aspace)
+{
+	struct msm_gem_vma *vma = lookup_vma(obj, aspace);
+
+	if (!vma)
+		return 0;
+
+	if (msm_gem_vma_inuse(vma))
+		return -EBUSY;
+
+	msm_gem_purge_vma(vma->aspace, vma);
+	msm_gem_close_vma(vma->aspace, vma);
+	del_vma(vma);
+
+	return 0;
+}
+
+/*
+ * Get the requested iova but don't pin it.  Fails if the requested iova is
+ * not available.  Doesn't need a put because iovas are currently valid for
+ * the life of the object.
+ *
+ * Setting an iova of zero will clear the vma.
+ */
+int msm_gem_set_iova(struct drm_gem_object *obj,
+		     struct msm_gem_address_space *aspace, uint64_t iova)
+{
+	int ret = 0;
+
+	msm_gem_lock(obj);
+	if (!iova) {
+		ret = clear_iova(obj, aspace);
+	} else {
+		struct msm_gem_vma *vma;
+		vma = get_vma_locked(obj, aspace, iova, iova + obj->size);
+		if (IS_ERR(vma)) {
+			ret = PTR_ERR(vma);
+		} else if (GEM_WARN_ON(vma->iova != iova)) {
+			clear_iova(obj, aspace);
+			ret = -EBUSY;
+		}
+	}
+	msm_gem_unlock(obj);
+
+	return ret;
+}
+
 /*
  * Unpin a iova by updating the reference counts. The memory isn't actually
  * purged until something else (shrinker, mm_notifier, destroy, etc) decides