[RFC PATCH 1/2] drm/amdgpu: Fix memory corruption due to swapout and swapin

[xinhui pan]

cpu 1                                           cpu 2
kfd alloc BO A(userptr)                         alloc BO B(GTT)
    ->init -> validate				-> init -> validate -> populate
    init_user_pages				  -> swapout BO A //hit ttm pages limit
	-> get_user_pages (fill up ttm->pages)
	 -> validate -> populate
          -> swapin BO A // Now hit the BUG

We know that get_user_pages may race with swapout on same BO.
Threre are some issues I have met.
1) memory corruption.
This is because we do a swap before memory is setup. ttm_tt_swapout()
just create a swap_storage with its content being 0x0. So when we setup
memory after the swapout. The following swapin makes the memory
corrupted.

2) panic
When swapout happes with get_user_pages, they touch ttm->pages without
anylock. It causes memory corruption too. But I hit page fault mostly.

Signed-off-by: xinhui pan <xinhui.pan at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index 928e8d57cd08..42460e4480f8 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -835,6 +835,7 @@ static int init_user_pages(struct kgd_mem *mem, uint64_t user_addr)
 	struct amdkfd_process_info *process_info = mem->process_info;
 	struct amdgpu_bo *bo = mem->bo;
 	struct ttm_operation_ctx ctx = { true, false };
+	struct page **pages;
 	int ret = 0;
 
 	mutex_lock(&process_info->lock);
@@ -852,7 +853,13 @@ static int init_user_pages(struct kgd_mem *mem, uint64_t user_addr)
 		goto out;
 	}
 
-	ret = amdgpu_ttm_tt_get_user_pages(bo, bo->tbo.ttm->pages);
+	pages = kvmalloc_array(bo->tbo.ttm->num_pages,
+			sizeof(struct page *),
+			GFP_KERNEL | __GFP_ZERO);
+	if (!pages)
+		goto unregister_out;
+
+	ret = amdgpu_ttm_tt_get_user_pages(bo, pages);
 	if (ret) {
 		pr_err("%s: Failed to get user pages: %d\n", __func__, ret);
 		goto unregister_out;
@@ -863,6 +870,12 @@ static int init_user_pages(struct kgd_mem *mem, uint64_t user_addr)
 		pr_err("%s: Failed to reserve BO\n", __func__);
 		goto release_out;
 	}
+
+	WARN_ON_ONCE(bo->tbo.ttm->page_flags & TTM_PAGE_FLAG_SWAPPED);
+
+	memcpy(bo->tbo.ttm->pages,
+			pages,
+			sizeof(struct page*) * bo->tbo.ttm->num_pages);
 	amdgpu_bo_placement_from_domain(bo, mem->domain);
 	ret = ttm_bo_validate(&bo->tbo, &bo->placement, &ctx);
 	if (ret)
@@ -872,6 +885,7 @@ static int init_user_pages(struct kgd_mem *mem, uint64_t user_addr)
 release_out:
 	amdgpu_ttm_tt_get_user_pages_done(bo->tbo.ttm);
 unregister_out:
+	kvfree(pages);
 	if (ret)
 		amdgpu_mn_unregister(bo);
 out:
-- 
2.25.1