drm/ttm: stop calling tt_swapin in vm_access

In commit:

commit 09ac4fcb
Author: Felix Kuehling <Felix.Kuehling@amd.com>
Date:   Thu Jul 13 17:01:16 2017 -0400

    drm/ttm: Implement vm_operations_struct.access v2

we added the vm_access hook, where we also directly call tt_swapin for
some reason. If something is swapped-out then the ttm_tt must also be
unpopulated, and since access_kmap should also call tt_populate, if
needed, then swapping-in will already be handled there.

If anything, calling tt_swapin directly here would likely always fail
since the tt->pages won't yet be populated, or worse since the tt->pages
array is never actually cleared in unpopulate this might lead to a nasty
uaf.

Fixes: 09ac4fcb ("drm/ttm: Implement vm_operations_struct.access v2")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Christian König <christian.koenig@amd.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210927114114.152310-1-matthew.auld@intel.comSigned-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -519,11 +519,6 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
 
 	switch (bo->resource->mem_type) {
 	case TTM_PL_SYSTEM:
-		if (unlikely(bo->ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
-			ret = ttm_tt_swapin(bo->ttm);
-			if (unlikely(ret != 0))
-				return ret;
-		}
 		fallthrough;
 	case TTM_PL_TT:
 		ret = ttm_bo_vm_access_kmap(bo, offset, buf, len, write);