drm/i915: Call i915_gem_evict_vm in vm_fault_gtt to prevent new ENOSPC errors, v2.

Now that we cannot unbind kill the currently locked object directly
because we're removing short term pinning, we may have to unbind the
object from gtt manually, using a i915_gem_evict_vm() call.

Changes since v1:
- Remove -ENOSPC warning, can still happen with concurrent mmaps
  where we can't unbind the other mmap because of the lock held.
  This  fixes the gem_mmap_gtt@cpuset tests.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220114132320.109030-2-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_mman.c

@@ -21,6 +21,7 @@
 #include "i915_trace.h"
 #include "i915_user_extensions.h"
 #include "i915_gem_ttm.h"
+#include "i915_gem_evict.h"
 #include "i915_vma.h"
 
 static inline bool
@@ -358,8 +359,21 @@ static vm_fault_t vm_fault_gtt(struct vm_fault *vmf)
 			vma = i915_gem_object_ggtt_pin_ww(obj, &ww, &view, 0, 0, flags);
 		}
 
-		/* The entire mappable GGTT is pinned? Unexpected! */
-		GEM_BUG_ON(vma == ERR_PTR(-ENOSPC));
+		/*
+		 * The entire mappable GGTT is pinned? Unexpected!
+		 * Try to evict the object we locked too, as normally we skip it
+		 * due to lack of short term pinning inside execbuf.
+		 */
+		if (vma == ERR_PTR(-ENOSPC)) {
+			ret = mutex_lock_interruptible(&ggtt->vm.mutex);
+			if (!ret) {
+				ret = i915_gem_evict_vm(&ggtt->vm);
+				mutex_unlock(&ggtt->vm.mutex);
+			}
+			if (ret)
+				goto err_reset;
+			vma = i915_gem_object_ggtt_pin_ww(obj, &ww, &view, 0, 0, flags);
+		}
 	}
 	if (IS_ERR(vma)) {
 		ret = PTR_ERR(vma);