Nouveau - Jul 2025 - [PATCH 0/2] drm/gpuvm+msm: Handle in-place remaps

turnip+msm uses a DUMP flag on the gpuva to indicate VA ranges to dump
(ie. for devcoredump).  In most cases (internal BOs like shader
instructions) this is known at the time the BO is MAPd, and the DUMP
flag can be set at the same time as the BO is initially bound into the
VM.  But for descriptor buffers, this isn't known until VkBuffer is
bound to the already mapped VkDeviceMemory, requiring an atomic remap
to set the flag.

The problem is that drmvm turns this into discreet unmap and remap
steps.  So there is a window where the VA is not mapped, which can
race with cmdstream exec (SUBMIT).

This series attempts to avoid that by turning an exact-remap into a
remap op instead, where the driver can handle the special case since
it can see both the unmap and map steps at the same time.

Rob Clark (2):
  drm/gpuvm: Send in-place re-maps to the driver as remap
  drm/msm: Handle in-place remaps

 drivers/gpu/drm/drm_gpuvm.c            | 21 +++++++++++++++++++++
 drivers/gpu/drm/msm/msm_gem_vma.c      | 17 +++++++++++++++--
 drivers/gpu/drm/nouveau/nouveau_uvmm.c |  3 ++-
 3 files changed, 38 insertions(+), 3 deletions(-)

-- 
2.50.1

The 'keep' hint on the unmap is only half useful, without being able to
link it to a map cb.  Instead combine the two ops into a remap op to
give the driver a chance to figure things out.

Signed-off-by: Rob Clark <robin.clark at oss.qualcomm.com>
---
In theory, drivers should treat an unmap+map combined in a remap step
the same as discreet unmap+map steps.

AFAICT nouveau is only driver using the keep hint, and this was missing
for the remap callback.  So I've added that.

But this is only tested on msm.

 drivers/gpu/drm/drm_gpuvm.c            | 21 +++++++++++++++++++++
 drivers/gpu/drm/nouveau/nouveau_uvmm.c |  3 ++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
index bbc7fecb6f4a..e21782a97fbe 100644
--- a/drivers/gpu/drm/drm_gpuvm.c
+++ b/drivers/gpu/drm/drm_gpuvm.c
@@ -2125,6 +2125,27 @@ __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
 				 offset == req_offset;
 
 			if (end == req_end) {
+				if (merge) {
+					/*
+					 * This is an exact remap of the existing
+					 * VA (potentially flags change)?  Pass
+					 * this to the driver as a remap so it can
+					 * do an in-place update:
+					 */
+					struct drm_gpuva_op_map n = {
+						.va.addr = va->va.addr,
+						.va.range = va->va.range,
+						.gem.obj = va->gem.obj,
+						.gem.offset = va->gem.offset,
+					};
+					struct drm_gpuva_op_unmap u = {
+						.va = va,
+						.keep = true,
+					};
+
+					return op_remap_cb(ops, priv, NULL, &n, &u);
+				}
+
 				ret = op_unmap_cb(ops, priv, va, merge);
 				if (ret)
 					return ret;
diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
index 48f105239f42..c3e3a15eb3c8 100644
--- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
@@ -820,7 +820,8 @@ op_remap(struct drm_gpuva_op_remap *r,
 	if (r->next)
 		end = r->next->va.addr;
 
-	op_unmap_range(u, addr, end - addr);
+	if (!u->keep)
+		op_unmap_range(u, addr, end - addr);
 }
 
 static int
-- 
2.50.1