[PATCH] drm/amd: fix debugfs access for discovery blob

[Mario Limonciello]

Accessing the blob for amdgpu discovery from debugfs triggers:

[ 1924.487667] kernel BUG at mm/usercopy.c:102!

usercopy_abort() explains that it needs to be solved by creating
a cache to store the data.

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2748#note_2023519
Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu.h         |  7 +++++--
 drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 17 ++++++++++++++++-
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c     |  2 ++
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index a3b86b86dc477..66a2251bdeba4 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -791,8 +791,11 @@ struct amdgpu_device {
 	bool				accel_working;
 	struct notifier_block		acpi_nb;
 	struct amdgpu_i2c_chan		*i2c_bus[AMDGPU_MAX_I2C_BUS];
-	struct debugfs_blob_wrapper     debugfs_vbios_blob;
-	struct debugfs_blob_wrapper     debugfs_discovery_blob;
+#if defined(CONFIG_DEBUG_FS)
+	struct debugfs_blob_wrapper	debugfs_vbios_blob;
+	struct debugfs_blob_wrapper	debugfs_discovery_blob;
+	struct kmem_cache		*discovery_blob_cache;
+#endif
 	struct mutex			srbm_mutex;
 	/* GRBM index mutex. Protects concurrent access to GRBM index */
 	struct mutex                    grbm_idx_mutex;
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
index 56e89e76ff179..55ea5be14b188 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
@@ -2180,7 +2180,15 @@ int amdgpu_debugfs_init(struct amdgpu_device *adev)
 	debugfs_create_blob("amdgpu_vbios", 0444, root,
 			    &adev->debugfs_vbios_blob);
 
-	adev->debugfs_discovery_blob.data = adev->mman.discovery_bin;
+
+	adev->discovery_blob_cache = kmem_cache_create_usercopy("amdgpu_discovery",
+								adev->mman.discovery_tmr_size,
+								0, 0, 0,
+								adev->mman.discovery_tmr_size,
+								NULL);
+	adev->debugfs_discovery_blob.data = kmem_cache_alloc(adev->discovery_blob_cache, GFP_KERNEL);
+	memcpy(adev->debugfs_discovery_blob.data, adev->mman.discovery_bin,
+	       adev->mman.discovery_tmr_size);
 	adev->debugfs_discovery_blob.size = adev->mman.discovery_tmr_size;
 	debugfs_create_blob("amdgpu_discovery", 0444, root,
 			    &adev->debugfs_discovery_blob);
@@ -2188,6 +2196,12 @@ int amdgpu_debugfs_init(struct amdgpu_device *adev)
 	return 0;
 }
 
+void amdgpu_debugfs_fini(struct amdgpu_device *adev)
+{
+	kmem_cache_free(adev->discovery_blob_cache, adev->debugfs_discovery_blob.data);
+	kmem_cache_destroy(adev->discovery_blob_cache);
+}
+
 #else
 int amdgpu_debugfs_init(struct amdgpu_device *adev)
 {
@@ -2197,4 +2211,5 @@ int amdgpu_debugfs_regs_init(struct amdgpu_device *adev)
 {
 	return 0;
 }
+inline void amdgpu_debugfs_fini(struct amdgpu_device *adev) {}
 #endif
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index 0593ef8fe0a63..1a3b30dff5171 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -2276,6 +2276,8 @@ amdgpu_pci_remove(struct pci_dev *pdev)
 	struct drm_device *dev = pci_get_drvdata(pdev);
 	struct amdgpu_device *adev = drm_to_adev(dev);
 
+	amdgpu_debugfs_fini(adev);
+
 	amdgpu_xcp_dev_unplug(adev);
 	drm_dev_unplug(dev);
 
-- 
2.34.1