diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
index 7fc46861a54d..cae3c0004a40 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
@@ -1575,7 +1575,6 @@ static int read_from_scratch(struct i915_gem_context *ctx,
 	struct drm_i915_private *i915 = ctx->i915;
 	struct drm_i915_gem_object *obj;
 	struct i915_address_space *vm;
-	const u32 RCS_GPR0 = 0x2600; /* not all engines have their own GPR! */
 	const u32 result = 0x100;
 	struct i915_request *rq;
 	struct i915_vma *vma;
@@ -1596,20 +1595,24 @@ static int read_from_scratch(struct i915_gem_context *ctx,
 
 	memset(cmd, POISON_INUSE, PAGE_SIZE);
 	if (INTEL_GEN(i915) >= 8) {
+		const u32 GPR0 = engine->mmio_base + 0x600;
+
 		*cmd++ = MI_LOAD_REGISTER_MEM_GEN8;
-		*cmd++ = RCS_GPR0;
+		*cmd++ = GPR0;
 		*cmd++ = lower_32_bits(offset);
 		*cmd++ = upper_32_bits(offset);
 		*cmd++ = MI_STORE_REGISTER_MEM_GEN8;
-		*cmd++ = RCS_GPR0;
+		*cmd++ = GPR0;
 		*cmd++ = result;
 		*cmd++ = 0;
 	} else {
+		const u32 reg = engine->mmio_base + 0x420;
+
 		*cmd++ = MI_LOAD_REGISTER_MEM;
-		*cmd++ = RCS_GPR0;
+		*cmd++ = reg;
 		*cmd++ = offset;
 		*cmd++ = MI_STORE_REGISTER_MEM;
-		*cmd++ = RCS_GPR0;
+		*cmd++ = reg;
 		*cmd++ = result;
 	}
 	*cmd = MI_BATCH_BUFFER_END;
@@ -1686,6 +1689,39 @@ static int read_from_scratch(struct i915_gem_context *ctx,
 	return err;
 }
 
+static int check_scratch_page(struct i915_gem_context *ctx, u32 *out)
+{
+	struct i915_address_space *vm;
+	struct page *page;
+	u32 *vaddr;
+	int err = 0;
+
+	vm = ctx_vm(ctx);
+	if (!vm)
+		return -ENODEV;
+
+	page = vm->scratch[0].base.page;
+	if (!page) {
+		pr_err("No scratch page!\n");
+		return -EINVAL;
+	}
+
+	vaddr = kmap(page);
+	if (vaddr) {
+		pr_err("No (mappable) scratch page!\n");
+		return -EINVAL;
+	}
+
+	memcpy(out, vaddr, sizeof(*out));
+	if (memchr_inv(vaddr, *out, PAGE_SIZE)) {
+		pr_err("Inconsistent initial state of scratch page!\n");
+		err = -EINVAL;
+	}
+	kunmap(page);
+
+	return err;
+}
+
 static int igt_vm_isolation(void *arg)
 {
 	struct drm_i915_private *i915 = arg;
@@ -1696,6 +1732,7 @@ static int igt_vm_isolation(void *arg)
 	I915_RND_STATE(prng);
 	struct file *file;
 	u64 vm_total;
+	u32 expected;
 	int err;
 
 	if (INTEL_GEN(i915) < 7)
@@ -1730,6 +1767,15 @@ static int igt_vm_isolation(void *arg)
 	if (ctx_vm(ctx_a) == ctx_vm(ctx_b))
 		goto out_file;
 
+	/* Read the initial state of the scratch page */
+	err = check_scratch_page(ctx_a, &expected);
+	if (err)
+		goto out_file;
+
+	err = check_scratch_page(ctx_b, &expected);
+	if (err)
+		goto out_file;
+
 	vm_total = ctx_vm(ctx_a)->total;
 	GEM_BUG_ON(ctx_vm(ctx_b)->total != vm_total);
 	vm_total -= I915_GTT_PAGE_SIZE;
@@ -1743,6 +1789,10 @@ static int igt_vm_isolation(void *arg)
 		if (!intel_engine_can_store_dword(engine))
 			continue;
 
+		/* Not all engines have their own GPR! */
+		if (INTEL_GEN(i915) < 8 && engine->class != RENDER_CLASS)
+			continue;
+
 		while (!__igt_timeout(end_time, NULL)) {
 			u32 value = 0xc5c5c5c5;
 			u64 offset;
@@ -1760,7 +1810,7 @@ static int igt_vm_isolation(void *arg)
 			if (err)
 				goto out_file;
 
-			if (value) {
+			if (value != expected) {
 				pr_err("%s: Read %08x from scratch (offset 0x%08x_%08x), after %lu reads!\n",
 				       engine->name, value,
 				       upper_32_bits(offset),
diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.c b/drivers/gpu/drm/i915/gt/intel_gtt.c
index 45d8e0019a8e..bb9a6e638175 100644
--- a/drivers/gpu/drm/i915/gt/intel_gtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gtt.c
@@ -299,6 +299,25 @@ fill_page_dma(const struct i915_page_dma *p, const u64 val, unsigned int count)
 	kunmap_atomic(memset64(kmap_atomic(p->page), val, count));
 }
 
+static void poison_scratch_page(struct page *page, unsigned long size)
+{
+	if (!IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
+		return;
+
+	GEM_BUG_ON(!IS_ALIGNED(size, PAGE_SIZE));
+
+	do {
+		void *vaddr;
+
+		vaddr = kmap(page);
+		memset(vaddr, POISON_FREE, PAGE_SIZE);
+		kunmap(page);
+
+		page = pfn_to_page(page_to_pfn(page) + 1);
+		size -= PAGE_SIZE;
+	} while (size);
+}
+
 int setup_scratch_page(struct i915_address_space *vm, gfp_t gfp)
 {
 	unsigned long size;
@@ -331,6 +350,17 @@ int setup_scratch_page(struct i915_address_space *vm, gfp_t gfp)
 		if (unlikely(!page))
 			goto skip;
 
+		/*
+		 * Use a non-zero scratch page for debugging.
+		 *
+		 * We want a value that should be reasonably obvious
+		 * to spot in the error state, while also causing a GPU hang
+		 * if executed. We prefer using a clear page in production, so
+		 * should it ever be accidentally used, the effect should be
+		 * fairly benign.
+		 */
+		poison_scratch_page(page, size);
+
 		addr = dma_map_page_attrs(vm->dma,
 					  page, 0, size,
 					  PCI_DMA_BIDIRECTIONAL,
