linux-kernel - [PATCH v2] drm/msm: Handle in-place remaps

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Message-ID: <20250805164431.24350-1-robin.clark@oss.qualcomm.com>
Date: Tue,  5 Aug 2025 09:44:31 -0700
From: Rob Clark <robin.clark@....qualcomm.com>
To: dri-devel@...ts.freedesktop.org
Cc: linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        Danilo Krummrich <dakr@...nel.org>,
        Connor Abbott <cwabbott0@...il.com>,
        Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2] drm/msm: Handle in-place remaps

Detect and handle the special case of a MAP op simply updating the vma
flags of an existing vma, and skip the pgtable updates.  This allows
turnip to set the MSM_VMA_DUMP flag on an existing mapping without
requiring additional synchronization against commands running on the
GPU.

Signed-off-by: Rob Clark <robin.clark@....qualcomm.com>
---
 drivers/gpu/drm/msm/msm_gem_vma.c | 41 ++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gem_vma.c b/drivers/gpu/drm/msm/msm_gem_vma.c
index d1f5bb2e0a16..00d0f3b7ba32 100644
--- a/drivers/gpu/drm/msm/msm_gem_vma.c
+++ b/drivers/gpu/drm/msm/msm_gem_vma.c
@@ -451,6 +451,8 @@ msm_gem_vm_bo_validate(struct drm_gpuvm_bo *vm_bo, struct drm_exec *exec)
 struct op_arg {
 	unsigned flags;
 	struct msm_vm_bind_job *job;
+	const struct msm_vm_bind_op *op;
+	bool kept;
 };
 
 static void
@@ -472,14 +474,18 @@ vma_from_op(struct op_arg *arg, struct drm_gpuva_op_map *op)
 }
 
 static int
-msm_gem_vm_sm_step_map(struct drm_gpuva_op *op, void *arg)
+msm_gem_vm_sm_step_map(struct drm_gpuva_op *op, void *_arg)
 {
-	struct msm_vm_bind_job *job = ((struct op_arg *)arg)->job;
+	struct op_arg *arg = _arg;
+	struct msm_vm_bind_job *job = arg->job;
 	struct drm_gem_object *obj = op->map.gem.obj;
 	struct drm_gpuva *vma;
 	struct sg_table *sgt;
 	unsigned prot;
 
+	if (arg->kept)
+		return 0;
+
 	vma = vma_from_op(arg, &op->map);
 	if (WARN_ON(IS_ERR(vma)))
 		return PTR_ERR(vma);
@@ -599,15 +605,41 @@ msm_gem_vm_sm_step_remap(struct drm_gpuva_op *op, void *arg)
 }
 
 static int
-msm_gem_vm_sm_step_unmap(struct drm_gpuva_op *op, void *arg)
+msm_gem_vm_sm_step_unmap(struct drm_gpuva_op *op, void *_arg)
 {
-	struct msm_vm_bind_job *job = ((struct op_arg *)arg)->job;
+	struct op_arg *arg = _arg;
+	struct msm_vm_bind_job *job = arg->job;
 	struct drm_gpuva *vma = op->unmap.va;
 	struct msm_gem_vma *msm_vma = to_msm_vma(vma);
 
 	vm_dbg("%p:%p:%p: %016llx %016llx", vma->vm, vma, vma->gem.obj,
 	       vma->va.addr, vma->va.range);
 
+	/*
+	 * Detect in-place remap.  Turnip does this to change the vma flags,
+	 * in particular MSM_VMA_DUMP.  In this case we want to avoid actually
+	 * touching the page tables, as that would require synchronization
+	 * against SUBMIT jobs running on the GPU.
+	 */
+	if (op->unmap.keep &&
+	    (arg->op->op == MSM_VM_BIND_OP_MAP) &&
+	    (vma->gem.obj == arg->op->obj) &&
+	    (vma->gem.offset == arg->op->obj_offset) &&
+	    (vma->va.addr == arg->op->iova) &&
+	    (vma->va.range == arg->op->range)) {
+		/* We are only expecting a single in-place unmap+map cb pair: */
+		WARN_ON(arg->kept);
+
+		/* Leave the existing VMA in place, but signal that to the map cb: */
+		arg->kept = true;
+
+		/* Only flags are changing, so update that in-place: */
+		unsigned orig_flags = vma->flags & (DRM_GPUVA_USERBITS - 1);
+		vma->flags = orig_flags | arg->flags;
+
+		return 0;
+	}
+
 	if (!msm_vma->mapped)
 		goto out_close;
 
@@ -1268,6 +1300,7 @@ vm_bind_job_prepare(struct msm_vm_bind_job *job)
 		const struct msm_vm_bind_op *op = &job->ops[i];
 		struct op_arg arg = {
 			.job = job,
+			.op = op,
 		};
 
 		switch (op->op) {
-- 
2.50.1