[PATCH 5/8] drm/i915/selftests: Check for incomplete LRI from the context image

[Ramalingam C]

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

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
interpretting 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 accesisble registers.)

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

Reported-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Ramalingam C <ramalingam.c at intel.com>
---
 drivers/gpu/drm/i915/gt/selftest_lrc.c | 63 ++++++++++++++++++++++----
 1 file changed, 55 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
index 2149b2c92793..6717ecaed178 100644
--- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
+++ b/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);
@@ -180,7 +183,7 @@ 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;
@@ -948,21 +951,43 @@ store_context(struct intel_context *ce,
 	hw = defaults;
 	hw += LRC_STATE_OFFSET / sizeof(*hw);
 	do {
-		u32 len = hw[dw] & 0x7f;
+		u32 len = hw[dw] & LRI_LENGTH_MASK;
 		u32 cmd = MI_STORE_REGISTER_MEM_GEN8;
 		u32 offset = 0;
 		u32 mask = ~0;
 
+		/*
+		 * 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",
+			       engine->name);
+			igt_hexdump(defaults, PAGE_SIZE);
+			break;
+		}
+
 		if (hw[dw] & MI_LRI_LRM_CS_MMIO) {
 			mask = 0xfff;
 			if (relative)
@@ -1162,21 +1187,32 @@ load_context(struct intel_context *ce,
 	hw = defaults;
 	hw += LRC_STATE_OFFSET / sizeof(*hw);
 	do {
-		u32 cmd = MI_INSTR(0x22, 0);
-		u32 len = hw[dw] & 0x7f;
+		u32 len = hw[dw] & LRI_LENGTH_MASK;
+		u32 cmd = LRI_HEADER;
 		u32 offset = 0;
 		u32 mask = ~0;
 
+		/* 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;
+		}
+
 		if (hw[dw] & MI_LRI_LRM_CS_MMIO) {
 			mask = 0xfff;
 			if (relative)
@@ -1327,19 +1363,30 @@ 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;
 		bool is_relative = relative;
 
+		/* 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;
+		}
+
 		if (!(hw[dw] & MI_LRI_LRM_CS_MMIO))
 			is_relative = false;
 
-- 
2.20.1