[PATCH v4 3/6] drm/amdgpu: implement synchronous TTM eviction for SVM BOs

[Junhua Shen <Junhua.Shen@amd.com>]

Implement the TTM eviction path for SVM (Shared Virtual Memory) BOs,
enabling VRAM overcommit scenarios where device-private pages must be
migrated back to system memory when VRAM is full.

- amdgpu_ttm.c: Add SVM BO detection in amdgpu_evict_flags() to evict
  directly to SYSTEM domain. Add SVM BO handling in amdgpu_bo_move()
  to call amdgpu_svm_bo_evict() for VRAM->SYSTEM transitions, which
  synchronously migrates device-private pages back to RAM via
  SDMA.

- amdgpu_migrate.c: Add amdgpu_svm_bo_evict() and
  amdgpu_svm_bo_is_svm() helpers.

- amdgpu_object.c: Register SVM BO destroy callback in
  amdgpu_bo_is_amdgpu_bo() so TTM eviction can identify and handle
  SVM BOs correctly.

Signed-off-by: Junhua Shen <Junhua.Shen@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.c | 28 +++++++++++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.h | 12 +++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_object.c  |  4 ++-
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c     | 20 +++++++++++++++
 4 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.c
index 54253d4dcc8d..ff45489c458e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.c
@@ -628,6 +628,34 @@ static const struct drm_pagemap_devmem_ops amdgpu_pagemap_ops = {
 	.copy_to_ram         = amdgpu_svm_copy_to_ram,
 };
 
+/**
+ * amdgpu_svm_bo_evict - Evict SVM BO by migrating device pages back to RAM
+ * @bo: The amdgpu_bo to evict (must be an amdgpu_bo_svm)
+ *
+ * Called from amdgpu_bo_move() when TTM needs to evict a SVM BO from VRAM.
+ * Uses drm_pagemap_evict_to_ram() to synchronously migrate all device-private
+ * pages back to system memory via SDMA.
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+int amdgpu_svm_bo_evict(struct amdgpu_bo *bo)
+{
+	struct amdgpu_bo_svm *sbo = to_amdgpu_bo_svm(bo);
+
+	return drm_pagemap_evict_to_ram(&sbo->devmem);
+}
+
+/**
+ * amdgpu_svm_bo_is_svm - Check if a TTM BO is an SVM BO
+ * @tbo: TTM buffer object
+ *
+ * Return: true if this is an amdgpu_bo_svm (identified by destroy callback)
+ */
+bool amdgpu_svm_bo_is_svm(struct ttm_buffer_object *tbo)
+{
+	return tbo->destroy == &amdgpu_bo_svm_destroy;
+}
+
 /* drm_pagemap_ops — top-level migration entry points */
 
 /**
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.h
index 75796983f6a5..63da96c17e27 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.h
@@ -29,6 +29,8 @@
 #include <linux/memremap.h>
 
 struct amdgpu_device;
+struct amdgpu_bo;
+struct ttm_buffer_object;
 
 /*
  * AMDGPU_INTERCONNECT_VRAM - Protocol identifier for local VRAM access.
@@ -78,12 +80,22 @@ struct amdgpu_pagemap {
 
 #if IS_ENABLED(CONFIG_DRM_AMDGPU_SVM)
 int amdgpu_svm_migration_init(struct amdgpu_device *adev);
+int amdgpu_svm_bo_evict(struct amdgpu_bo *bo);
+bool amdgpu_svm_bo_is_svm(struct ttm_buffer_object *tbo);
 #else
 static inline
 int amdgpu_svm_migration_init(struct amdgpu_device *adev)
 {
 	return 0;
 }
+static inline int amdgpu_svm_bo_evict(struct amdgpu_bo *bo)
+{
+	return -ENODEV;
+}
+static inline bool amdgpu_svm_bo_is_svm(struct ttm_buffer_object *tbo)
+{
+	return false;
+}
 #endif
 
 /**
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
index 1fb956400696..78a677ff32bf 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
@@ -43,6 +43,7 @@
 #include "amdgpu_vram_mgr.h"
 #include "amdgpu_vm.h"
 #include "amdgpu_dma_buf.h"
+#include "amdgpu_migrate.h"
 
 /**
  * DOC: amdgpu_object
@@ -93,7 +94,8 @@ static void amdgpu_bo_user_destroy(struct ttm_buffer_object *tbo)
 bool amdgpu_bo_is_amdgpu_bo(struct ttm_buffer_object *bo)
 {
 	if (bo->destroy == &amdgpu_bo_destroy ||
-	    bo->destroy == &amdgpu_bo_user_destroy)
+	    bo->destroy == &amdgpu_bo_user_destroy ||
+	    amdgpu_svm_bo_is_svm(bo))
 		return true;
 
 	return false;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 714fd8d12ca5..5a45a29ef051 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -59,6 +59,7 @@
 #include "amdgpu_hmm.h"
 #include "amdgpu_atomfirmware.h"
 #include "amdgpu_res_cursor.h"
+#include "amdgpu_migrate.h"
 #include "bif/bif_4_1_d.h"
 
 MODULE_IMPORT_NS("DMA_BUF");
@@ -118,6 +119,15 @@ static void amdgpu_evict_flags(struct ttm_buffer_object *bo,
 		return;
 	}
 
+	/* SVM BOs must evict directly to system memory for drm_pagemap
+	 * migration back to RAM in amdgpu_bo_move().
+	 */
+	if (amdgpu_svm_bo_is_svm(bo)) {
+		amdgpu_bo_placement_from_domain(abo, AMDGPU_GEM_DOMAIN_CPU);
+		*placement = abo->placement;
+		return;
+	}
+
 	switch (bo->resource->mem_type) {
 	case AMDGPU_PL_GDS:
 	case AMDGPU_PL_GWS:
@@ -568,6 +578,16 @@ static int amdgpu_bo_move(struct ttm_buffer_object *bo, bool evict,
 		abo->flags &= ~AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
 	}
 
+	/* SVM BO eviction: migrate device-private pages back to RAM */
+	if (amdgpu_svm_bo_is_svm(bo) &&
+	    old_mem->mem_type == TTM_PL_VRAM &&
+	    new_mem->mem_type == TTM_PL_SYSTEM) {
+		r = amdgpu_svm_bo_evict(abo);
+		if (!r)
+			ttm_bo_move_null(bo, new_mem);
+		return r;
+	}
+
 	if (adev->mman.buffer_funcs_enabled &&
 	    ((old_mem->mem_type == TTM_PL_SYSTEM &&
 	      new_mem->mem_type == TTM_PL_VRAM) ||
-- 
2.34.1