drm/i915/selftests: Check for incomplete LRI from the context image

In order to keep the context image parser simple, we assume that all
commands follow a similar format. A few, especially not MI commands on
the render engines, have fixed lengths not encoded in a length field.
This caused us to incorrectly skip over 3D state commands, and start
interpreting context data as instructions. Eventually, as Daniele
discovered, this would lead us to find addition LRI as part of the data
and mistakenly add invalid LRI commands to the context probes.

Stop parsing after we see the first !MI command, as we know we will have
seen all the context registers by that point. (Mostly true for all gen
so far, though the render context does have LRI after the first page
that we have been ignoring so far. It would be useful to extract those
as well so that we have the full list of user accessible registers.)

Similarly, emit a warning if we do try to emit an invalid zero-length
LRI.

Testcase: igt@i915_selftest@live@gt_lrc
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6580
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/6670Reported-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Acked-by: Thomas Hellstrom <thomas.hellstrom@linux.intel.com>
Signed-off-by: Karolina Drobnik <karolina.drobnik@intel.com>
Reviewed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7377cb3b371a983dce02be69f6611fcf85c822bb.1663081418.git.karolina.drobnik@intel.com

drivers/gpu/drm/i915/gt/selftest_lrc.c

@@ -27,6 +27,9 @@
 #define NUM_GPR 16
 #define NUM_GPR_DW (NUM_GPR * 2) /* each GPR is 2 dwords */
 
+#define LRI_HEADER MI_INSTR(0x22, 0)
+#define LRI_LENGTH_MASK GENMASK(7, 0)
+
 static struct i915_vma *create_scratch(struct intel_gt *gt)
 {
 	return __vm_create_scratch_for_read_pinned(&gt->ggtt->vm, PAGE_SIZE);
@@ -202,7 +205,7 @@ static int live_lrc_layout(void *arg)
 				continue;
 			}
 
-			if ((lri & GENMASK(31, 23)) != MI_INSTR(0x22, 0)) {
+			if ((lri & GENMASK(31, 23)) != LRI_HEADER) {
 				pr_err("%s: Expected LRI command at dword %d, found %08x\n",
 				       engine->name, dw, lri);
 				err = -EINVAL;
@@ -992,18 +995,40 @@ store_context(struct intel_context *ce, struct i915_vma *scratch)
 	hw = defaults;
 	hw += LRC_STATE_OFFSET / sizeof(*hw);
 	do {
-		u32 len = hw[dw] & 0x7f;
+		u32 len = hw[dw] & LRI_LENGTH_MASK;
+
+		/*
+		 * Keep it simple, skip parsing complex commands
+		 *
+		 * At present, there are no more MI_LOAD_REGISTER_IMM
+		 * commands after the first 3D state command. Rather
+		 * than include a table (see i915_cmd_parser.c) of all
+		 * the possible commands and their instruction lengths
+		 * (or mask for variable length instructions), assume
+		 * we have gathered the complete list of registers and
+		 * bail out.
+		 */
+		if ((hw[dw] >> INSTR_CLIENT_SHIFT) != INSTR_MI_CLIENT)
+			break;
 
 		if (hw[dw] == 0) {
 			dw++;
 			continue;
 		}
 
-		if ((hw[dw] & GENMASK(31, 23)) != MI_INSTR(0x22, 0)) {
+		if ((hw[dw] & GENMASK(31, 23)) != LRI_HEADER) {
+			/* Assume all other MI commands match LRI length mask */
 			dw += len + 2;
 			continue;
 		}
 
+		if (!len) {
+			pr_err("%s: invalid LRI found in context image\n",
+			       ce->engine->name);
+			igt_hexdump(defaults, PAGE_SIZE);
+			break;
+		}
+
 		dw++;
 		len = (len + 1) / 2;
 		while (len--) {
@@ -1155,18 +1180,29 @@ static struct i915_vma *load_context(struct intel_context *ce, u32 poison)
 	hw = defaults;
 	hw += LRC_STATE_OFFSET / sizeof(*hw);
 	do {
-		u32 len = hw[dw] & 0x7f;
+		u32 len = hw[dw] & LRI_LENGTH_MASK;
+
+		/* For simplicity, break parsing at the first complex command */
+		if ((hw[dw] >> INSTR_CLIENT_SHIFT) != INSTR_MI_CLIENT)
+			break;
 
 		if (hw[dw] == 0) {
 			dw++;
 			continue;
 		}
 
-		if ((hw[dw] & GENMASK(31, 23)) != MI_INSTR(0x22, 0)) {
+		if ((hw[dw] & GENMASK(31, 23)) != LRI_HEADER) {
 			dw += len + 2;
 			continue;
 		}
 
+		if (!len) {
+			pr_err("%s: invalid LRI found in context image\n",
+			       ce->engine->name);
+			igt_hexdump(defaults, PAGE_SIZE);
+			break;
+		}
+
 		dw++;
 		len = (len + 1) / 2;
 		*cs++ = MI_LOAD_REGISTER_IMM(len);
@@ -1297,18 +1333,29 @@ static int compare_isolation(struct intel_engine_cs *engine,
 	hw = defaults;
 	hw += LRC_STATE_OFFSET / sizeof(*hw);
 	do {
-		u32 len = hw[dw] & 0x7f;
+		u32 len = hw[dw] & LRI_LENGTH_MASK;
+
+		/* For simplicity, break parsing at the first complex command */
+		if ((hw[dw] >> INSTR_CLIENT_SHIFT) != INSTR_MI_CLIENT)
+			break;
 
 		if (hw[dw] == 0) {
 			dw++;
 			continue;
 		}
 
-		if ((hw[dw] & GENMASK(31, 23)) != MI_INSTR(0x22, 0)) {
+		if ((hw[dw] & GENMASK(31, 23)) != LRI_HEADER) {
 			dw += len + 2;
 			continue;
 		}
 
+		if (!len) {
+			pr_err("%s: invalid LRI found in context image\n",
+			       engine->name);
+			igt_hexdump(defaults, PAGE_SIZE);
+			break;
+		}
+
 		dw++;
 		len = (len + 1) / 2;
 		while (len--) {