gpu: nvgpu: add FOREIGN_SGT mem flag

Add an internal flag NVGPU_MEM_FLAG_FOREIGN_SGT to specify that the sgt
member of an nvgpu_mem must not be freed when the nvgpu_mem is freed.

Bug 200145225
Bug 200541476

Change-Id: I044fb91a5f9d148f38fb0cbf63d0cdfd64a070ce
Signed-off-by: Konsta Holtta <kholtta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/1819801
Signed-off-by: Debarshi Dutta <ddutta@nvidia.com>
(cherry picked from commit 9de6d20abb8fef0cd11c22676846d809ee3f9afc
in dev-main)
Reviewed-on: https://git-master.nvidia.com/r/2170602
GVS: Gerrit_Virtual_Submit
Reviewed-by: Bibek Basu <bbasu@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

2 files changed, 12 insertions, 1 deletions

diff --git a/drivers/gpu/nvgpu/include/nvgpu/nvgpu_mem.h b/drivers/gpu/nvgpu/include/nvgpu/nvgpu_mem.h
index e69274b5..8e62a1d6 100644
--- a/drivers/gpu/nvgpu/include/nvgpu/nvgpu_mem.h
+++ b/drivers/gpu/nvgpu/include/nvgpu/nvgpu_mem.h
@@ -174,6 +174,15 @@ struct nvgpu_mem {
          * nvgpu_mem in a system specific way.
          */
 #define __NVGPU_MEM_FLAG_NO_DMA                  (1 << 3)
+        /*
+         * Some nvgpu_mem objects act as facades to memory buffers owned by
+         * someone else. This internal flag specifies that the sgt field is
+         * "borrowed", and it must not be freed by us.
+         *
+         * Of course the caller will have to make sure that the sgt owner
+         * outlives the nvgpu_mem.
+         */
+#define NVGPU_MEM_FLAG_FOREIGN_SGT               (1 << 4)
         unsigned long                            mem_flags;
 
         /*
diff --git a/drivers/gpu/nvgpu/os/linux/linux-dma.c b/drivers/gpu/nvgpu/os/linux/linux-dma.c
index 52987a87..d704b2a4 100644
--- a/drivers/gpu/nvgpu/os/linux/linux-dma.c
+++ b/drivers/gpu/nvgpu/os/linux/linux-dma.c
@@ -392,8 +392,10 @@ void nvgpu_dma_free_sys(struct gk20a *g, struct nvgpu_mem *mem)
         if (mem->mem_flags & __NVGPU_MEM_FLAG_NO_DMA)
                 nvgpu_kfree(g, mem->priv.pages);
 
-        if (mem->priv.sgt)
+        if ((mem->mem_flags & NVGPU_MEM_FLAG_FOREIGN_SGT) == 0 &&
+                        mem->priv.sgt != NULL) {
                 nvgpu_free_sgtable(g, &mem->priv.sgt);
+        }
 
         dma_dbg_free_done(g, mem->size, "sysmem");