linux-kernel - [PATCH v3 2/5] drm/nouveau/uvmm: Allow larger pages

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Message-ID: <20251030230357.45070-3-mohamedahmedegypt2001@gmail.com>
Date: Fri, 31 Oct 2025 01:03:54 +0200
From: Mohamed Ahmed <mohamedahmedegypt2001@...il.com>
To: linux-kernel@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org,
	Mary Guillemard <mary@...y.zone>,
	Faith Ekstrand <faith.ekstrand@...labora.com>,
	Lyude Paul <lyude@...hat.com>,
	Danilo Krummrich <dakr@...nel.org>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	nouveau@...ts.freedesktop.org,
	Mohamed Ahmed <mohamedahmedegypt2001@...il.com>
Subject: [PATCH v3 2/5] drm/nouveau/uvmm: Allow larger pages

From: Mary Guillemard <mary@...y.zone>

Now that everything in UVMM knows about the variable page shift, we can
select larger values.

The proposed approach relies on nouveau_bo::page unless if it would cause
alignment issues (in which case we fall back to searching for an
appropriate shift)

Signed-off-by: Mary Guillemard <mary@...y.zone>
Co-developed-by: Mohamed Ahmed <mohamedahmedegypt2001@...il.com>
Signed-off-by: Mohamed Ahmed <mohamedahmedegypt2001@...il.com>
---
 drivers/gpu/drm/nouveau/nouveau_uvmm.c | 60 +++++++++++++++++++++++++-
 1 file changed, 58 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
index 2cd0835b05e8..f2d032f665e8 100644
--- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
@@ -454,6 +454,62 @@ op_unmap_prepare_unwind(struct drm_gpuva *va)
 	drm_gpuva_insert(va->vm, va);
 }
 
+static bool
+op_map_aligned_to_page_shift(const struct drm_gpuva_op_map *op, u8 page_shift)
+{
+	u64 non_page_bits = (1ULL << page_shift) - 1;
+
+	return op->va.addr & non_page_bits == 0 &&
+	       op->va.range & non_page_bits == 0 &&
+	       op->gem.offset & non_page_bits == 0;
+}
+
+static u8
+select_page_shift(struct nouveau_uvmm *uvmm, struct drm_gpuva_op_map *op)
+{
+	struct nouveau_bo *nvbo = nouveau_gem_object(op->gem.obj);
+
+	/* nouveau_bo_fixup_align() guarantees that the page size will be aligned
+	 * for most cases, but it can't handle cases where userspace allocates with
+	 * a size and then binds with a smaller granularity. So in order to avoid
+	 * breaking old userspace, we need to ensure that the VA is actually
+	 * aligned before using it, and if it isn't, then we downgrade to the first
+	 * granularity that will fit, which is optimal from a correctness and
+	 * performance perspective.
+	 */
+	if (op_map_aligned_to_page_shift(op, nvbo->page))
+		return nvbo->page;
+
+	struct nouveau_mem *mem = nouveau_mem(nvbo->bo.resource);
+	struct nvif_vmm *vmm = &uvmm->vmm.vmm;
+	int i;
+
+	/* If the given granularity doesn't fit, let's find one that will fit. */
+	for (i = 0; i < vmm->page_nr; i++) {
+		/* Ignore anything that is bigger or identical to the BO preference. */
+		if (vmm->page[i].shift >= nvbo->page)
+			continue;
+
+		/* Skip incompatible domains. */
+		if ((mem->mem.type & NVIF_MEM_VRAM) && !vmm->page[i].vram)
+			continue;
+		if ((mem->mem.type & NVIF_MEM_HOST) &&
+		    (!vmm->page[i].host || vmm->page[i].shift > PAGE_SHIFT))
+			continue;
+
+		/* If it fits, return the proposed shift. */
+		if (op_map_aligned_to_page_shift(op, vmm->page[i].shift))
+			return vmm->page[i].shift;
+	}
+
+	/* If we get here then nothing can reconcile the requirements. This should never
+	 * happen.
+	 */
+	WARN_ON(1);
+
+	return PAGE_SHIFT;
+}
+
 static void
 nouveau_uvmm_sm_prepare_unwind(struct nouveau_uvmm *uvmm,
 			       struct nouveau_uvma_prealloc *new,
@@ -506,7 +562,7 @@ nouveau_uvmm_sm_prepare_unwind(struct nouveau_uvmm *uvmm,
 			if (vmm_get_range)
 				nouveau_uvmm_vmm_put(uvmm, vmm_get_start,
 						     vmm_get_range,
-						     PAGE_SHIFT);
+						     select_page_shift(uvmm, &op->map));
 			break;
 		}
 		case DRM_GPUVA_OP_REMAP: {
@@ -599,7 +655,7 @@ op_map_prepare(struct nouveau_uvmm *uvmm,
 
 	uvma->region = args->region;
 	uvma->kind = args->kind;
-	uvma->page_shift = PAGE_SHIFT;
+	uvma->page_shift = select_page_shift(uvmm, op);
 
 	drm_gpuva_map(&uvmm->base, &uvma->va, op);
 
-- 
2.51.1