From 488751a0ef9b5ce572c47301ce62d54fc6b5a74d Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 18 Jan 2021 09:53:32 +0000
Subject: [PATCH] drm/i915/gt: Prevent use of engine->wa_ctx after error
Git-commit: 488751a0ef9b5ce572c47301ce62d54fc6b5a74d
Patch-mainline: v5.11-rc5
References: git-fixes
Alt-commit: 5b4dc95cf7f573e927fbbd406ebe54225d41b9b2

On error we unpin and free the wa_ctx.vma, but do not clear any of the
derived flags. During lrc_init, we look at the flags and attempt to
dereference the wa_ctx.vma if they are set. To protect the error path
where we try to limp along without the wa_ctx, make sure we clear those
flags!

Reported-by: Matt Roper <matthew.d.roper@intel.com>
Fixes: 604a8f6f1e33 ("drm/i915/lrc: Only enable per-context and per-bb buffers if set")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: <stable@vger.kernel.org> # v4.15+
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210108204026.20682-1-chris@chris-wilson.co.uk
(cherry-picked from 5b4dc95cf7f573e927fbbd406ebe54225d41b9b2)

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210118095332.458813-1-chris@chris-wilson.co.uk
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 7614a3d24fca..26c7d0a50585 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -3988,6 +3988,9 @@ static int lrc_setup_wa_ctx(struct intel_engine_cs *engine)
 static void lrc_destroy_wa_ctx(struct intel_engine_cs *engine)
 {
 	i915_vma_unpin_and_release(&engine->wa_ctx.vma, 0);
+
+	/* Called on error unwind, clear all flags to prevent further use */
+	memset(&engine->wa_ctx, 0, sizeof(engine->wa_ctx));
 }
 
 typedef u32 *(*wa_bb_func_t)(struct intel_engine_cs *engine, u32 *batch);
-- 
2.26.2