[PATCH 5.10 025/142] drm/i915/gt: Always try to reserve GGTT address 0x0

Greg Kroah-Hartman
2021-02-02T20:05:49Z

From: Chris Wilson <chris@chris-wilson.co.uk>

commit 489140b5ba2e7cc4b853c29e0591895ddb462a82 upstream.

Since writing to address 0 is a very common mistake, let's try to avoid
putting anything sensitive there.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210125125033.23656-1-chris@chris-wilson.co.uk
Cc: stable@vger.kernel.org
(cherry picked from commit 56b429cc584c6ed8b895d8d8540959655db1ff73)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/i915/gt/intel_ggtt.c | 47 ++++++++++++++++++++++++++---------
1 file changed, 35 insertions(+), 12 deletions(-)

--- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
@@ -526,16 +526,39 @@ static int init_ggtt(struct i915_ggtt *g

mutex_init(&ggtt->error_mutex);
if (ggtt->mappable_end) {
- /* Reserve a mappable slot for our lockless error capture */
- ret = drm_mm_insert_node_in_range(&ggtt->vm.mm,
- &ggtt->error_capture,
- PAGE_SIZE, 0,
- I915_COLOR_UNEVICTABLE,
- 0, ggtt->mappable_end,
- DRM_MM_INSERT_LOW);
- if (ret)
- return ret;
+ /*
+ * Reserve a mappable slot for our lockless error capture.
+ *
+ * We strongly prefer taking address 0x0 in order to protect
+ * other critical buffers against accidental overwrites,
+ * as writing to address 0 is a very common mistake.
+ *
+ * Since 0 may already be in use by the system (e.g. the BIOS
+ * framebuffer), we let the reservation fail quietly and hope
+ * 0 remains reserved always.
+ *
+ * If we fail to reserve 0, and then fail to find any space
+ * for an error-capture, remain silent. We can afford not
+ * to reserve an error_capture node as we have fallback
+ * paths, and we trust that 0 will remain reserved. However,
+ * the only likely reason for failure to insert is a driver
+ * bug, which we expect to cause other failures...
+ */
+ ggtt->error_capture.size = I915_GTT_PAGE_SIZE;
+ ggtt->error_capture.color = I915_COLOR_UNEVICTABLE;
+ if (drm_mm_reserve_node(&ggtt->vm.mm, &ggtt->error_capture))
+ drm_mm_insert_node_in_range(&ggtt->vm.mm,
+ &ggtt->error_capture,
+ ggtt->error_capture.size, 0,
+ ggtt->error_capture.color,
+ 0, ggtt->mappable_end,
+ DRM_MM_INSERT_LOW);
}
+ if (drm_mm_node_allocated(&ggtt->error_capture))
+ drm_dbg(&ggtt->vm.i915->drm,
+ "Reserved GGTT:[%llx, %llx] for use by error capture\n",
+ ggtt->error_capture.start,
+ ggtt->error_capture.start + ggtt->error_capture.size);

/*
* The upper portion of the GuC address space has a sizeable hole
@@ -548,9 +571,9 @@ static int init_ggtt(struct i915_ggtt *g

/* Clear any non-preallocated blocks */
drm_mm_for_each_hole(entry, &ggtt->vm.mm, hole_start, hole_end) {
- drm_dbg_kms(&ggtt->vm.i915->drm,
- "clearing unused GTT space: [%lx, %lx]\n",
- hole_start, hole_end);
+ drm_dbg(&ggtt->vm.i915->drm,
+ "clearing unused GTT space: [%lx, %lx]\n",
+ hole_start, hole_end);
ggtt->vm.clear_range(&ggtt->vm, hole_start,
hole_end - hole_start);
}