[PATCH 2/3] drm/i915/selftests: Fix memory corruption in live_lrc_isolation

[Matthew Brost]

GuC submission has exposed an existing memory corruption in
live_lrc_isolation. We believe that some writes to the watchdog offsets
in the LRC (0x178 & 0x17c) can result in trashing of portions of the
address space. With GuC submission there are additional objects which
can move the context redzone into the space that is trashed. To
workaround this avoid poisoning the watchdog.

Signed-off-by: Matthew Brost <matthew.brost at intel.com>
---
 drivers/gpu/drm/i915/gt/selftest_lrc.c | 29 +++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
index b0977a3b699b..6500e9fce8a0 100644
--- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
+++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
@@ -1074,6 +1074,32 @@ record_registers(struct intel_context *ce,
 	goto err_after;
 }
 
+static u32 safe_offset(u32 offset, u32 reg)
+{
+	/* XXX skip testing of watchdog */
+	if (offset == 0x178 || offset == 0x17c)
+		reg = 0;
+
+	return reg;
+}
+
+static int get_offset_mask(struct intel_engine_cs *engine)
+{
+	if (GRAPHICS_VER(engine->i915) < 12)
+		return 0xfff;
+
+	switch (engine->class) {
+	default:
+	case RENDER_CLASS:
+		return 0x07ff;
+	case COPY_ENGINE_CLASS:
+		return 0x0fff;
+	case VIDEO_DECODE_CLASS:
+	case VIDEO_ENHANCEMENT_CLASS:
+		return 0x3fff;
+	}
+}
+
 static struct i915_vma *load_context(struct intel_context *ce, u32 poison)
 {
 	struct i915_vma *batch;
@@ -1117,7 +1143,8 @@ static struct i915_vma *load_context(struct intel_context *ce, u32 poison)
 		len = (len + 1) / 2;
 		*cs++ = MI_LOAD_REGISTER_IMM(len);
 		while (len--) {
-			*cs++ = hw[dw];
+			*cs++ = safe_offset(hw[dw] & get_offset_mask(ce->engine),
+					    hw[dw]);
 			*cs++ = poison;
 			dw += 2;
 		}
-- 
2.28.0