1 files changed, 26 insertions, 4 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index afe45cbcd762..9ea024395d49 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -580,10 +580,9 @@ setup_scratch_page(struct i915_address_space *vm, gfp_t gfp)
          * region, including any PTEs which happen to point to scratch.
          *
          * This is only relevant for the 48b PPGTT where we support
-         * huge-gtt-pages, see also i915_vma_insert().
-         *
-         * TODO: we should really consider write-protecting the scratch-page and
-         * sharing between ppgtt
+         * huge-gtt-pages, see also i915_vma_insert(). However, as we share the
+         * scratch (read-only) between all vm, we create one 64k scratch page
+         * for all.
          */
         size = I915_GTT_PAGE_SIZE_4K;
         if (i915_vm_is_48bit(vm) &&
@@ -1209,6 +1208,26 @@ static int gen8_init_scratch(struct i915_address_space *vm)
 {
         int ret;
 
+        /*
+         * If everybody agrees to not to write into the scratch page,
+         * we can reuse it for all vm, keeping contexts and processes separate.
+         */
+        if (vm->has_read_only &&
+            vm->i915->kernel_context &&
+            vm->i915->kernel_context->ppgtt) {
+                struct i915_address_space *clone =
+                        &vm->i915->kernel_context->ppgtt->vm;
+
+                GEM_BUG_ON(!clone->has_read_only);
+
+                vm->scratch_page.order = clone->scratch_page.order;
+                vm->scratch_pte = clone->scratch_pte;
+                vm->scratch_pt  = clone->scratch_pt;
+                vm->scratch_pd  = clone->scratch_pd;
+                vm->scratch_pdp = clone->scratch_pdp;
+                return 0;
+        }
+
         ret = setup_scratch_page(vm, __GFP_HIGHMEM);
         if (ret)
                 return ret;
@@ -1289,6 +1308,9 @@ static int gen8_ppgtt_notify_vgt(struct i915_hw_ppgtt *ppgtt, bool create)
 
 static void gen8_free_scratch(struct i915_address_space *vm)
 {
+        if (!vm->scratch_page.daddr)
+                return;
+
         if (use_4lvl(vm))
                 free_pdp(vm, vm->scratch_pdp);
         free_pd(vm, vm->scratch_pd);