[Intel-gfx] [PATCH v4 07/14] drm/ttm: add TTM_TT_FLAG_EXTERNAL_MAPPABLE

Matthew Auld
2021-09-21T11:02:18Z

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>
---
drivers/gpu/drm/ttm/ttm_bo_vm.c | 6 ++++--
drivers/gpu/drm/ttm/ttm_tt.c | 3 +++
include/drm/ttm/ttm_tt.h | 19 ++++++++++++++++---
3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 950f4f132802..33680c94127c 100644
--- 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 86f31fde6e35..7e83c00a3f48 100644
--- 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 f3ef568da651..5995b8ee1667 100644
--- a/include/drm/ttm/ttm_tt.h
+++ b/include/drm/ttm/ttm_tt.h
@@ -66,11 +66,24 @@ 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.
*/
-#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;
--
2.26.3