drm/ttm: add TTM_TT_FLAG_EXTERNAL_MAPPABLE

In commit:

commit 667a50db0477d47fdff01c666f5ee1ce26b5264c
Author: Thomas Hellstrom <thellstrom@vmware.com>
Date:   Fri Jan 3 11:17:18 2014 +0100

    drm/ttm: Refuse to fault (prime-) imported pages

we introduced the restriction that imported pages should not be directly
mappable through TTM(this also extends to userptr). In the next patch we
want to introduce a shmem_tt backend, which should follow all the
existing rules with TTM_PAGE_FLAG_EXTERNAL, since it will need to handle
swapping itself, but with the above mapping restriction lifted.

v2(Christian):
  - Don't OR together EXTERNAL and EXTERNAL_MAPPABLE in the definition
    of EXTERNAL_MAPPABLE, just leave it the caller to handle this
    correctly, otherwise we might encounter subtle issues.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210929132629.353541-3-matthew.auld@intel.com
Signed-off-by: Christian König <christian.koenig@amd.com>

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 950f4f1..33680c9 100644 (file)
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -163,8 +163,10 @@ vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
         * (if at all) by redirecting mmap to the exporter.
         */
        if (bo->ttm && (bo->ttm->page_flags & TTM_TT_FLAG_EXTERNAL)) {
-               dma_resv_unlock(bo->base.resv);
-               return VM_FAULT_SIGBUS;
+               if (!(bo->ttm->page_flags & TTM_TT_FLAG_EXTERNAL_MAPPABLE)) {
+                       dma_resv_unlock(bo->base.resv);
+                       return VM_FAULT_SIGBUS;
+               }
        }
 
        return 0;

diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index 86f31fd..7e83c00 100644 (file)
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -84,6 +84,9 @@ int ttm_tt_create(struct ttm_buffer_object *bo, bool zero_alloc)
        if (unlikely(bo->ttm == NULL))
                return -ENOMEM;
 
+       WARN_ON(bo->ttm->page_flags & TTM_TT_FLAG_EXTERNAL_MAPPABLE &&
+               !(bo->ttm->page_flags & TTM_TT_FLAG_EXTERNAL));
+
        return 0;
 }
 

diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
index 86d7406..f208321 100644 (file)
--- a/include/drm/ttm/ttm_tt.h
+++ b/include/drm/ttm/ttm_tt.h
@@ -67,13 +67,26 @@ struct ttm_tt {
         * Note that enum ttm_bo_type.ttm_bo_type_sg objects will always enable
         * this flag.
         *
+        * TTM_TT_FLAG_EXTERNAL_MAPPABLE: Same behaviour as
+        * TTM_TT_FLAG_EXTERNAL, but with the reduced restriction that it is
+        * still valid to use TTM to map the pages directly. This is useful when
+        * implementing a ttm_tt backend which still allocates driver owned
+        * pages underneath(say with shmem).
+        *
+        * Note that since this also implies TTM_TT_FLAG_EXTERNAL, the usage
+        * here should always be:
+        *
+        *   page_flags = TTM_TT_FLAG_EXTERNAL |
+        *                TTM_TT_FLAG_EXTERNAL_MAPPABLE;
+        *
         * TTM_TT_FLAG_PRIV_POPULATED: TTM internal only. DO NOT USE. This is
         * set by TTM after ttm_tt_populate() has successfully returned, and is
         * then unset when TTM calls ttm_tt_unpopulate().
         */
-#define TTM_TT_FLAG_SWAPPED    (1 << 0)
-#define TTM_TT_FLAG_ZERO_ALLOC (1 << 1)
-#define TTM_TT_FLAG_EXTERNAL   (1 << 2)
+#define TTM_TT_FLAG_SWAPPED            (1 << 0)
+#define TTM_TT_FLAG_ZERO_ALLOC         (1 << 1)
+#define TTM_TT_FLAG_EXTERNAL           (1 << 2)
+#define TTM_TT_FLAG_EXTERNAL_MAPPABLE  (1 << 3)
 
 #define TTM_TT_FLAG_PRIV_POPULATED  (1 << 31)
        uint32_t page_flags;