[Intel-gfx] [PATCH] drm/i915: Avoid mixing integer types during batch copies

[Chris Wilson]

Be consistent and use unsigned long throughout the chunk copies to
avoid the inherent clumsiness of mixing integer types of different
widths and signs. Failing to take acount of a wider unsigned type when
using min_t can lead to treating it as a negative, only for it flip back
to a large unsigned value after passing a boundary check.

Fixes: ed13033f0287 ("drm/i915/cmdparser: Only cache the dst vmap")
Testcase: igt/gen9_exec_parse/bb-large
Reported-by: "Candelaria, Jared" <jared.candelaria at intel.com>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: "Candelaria, Jared" <jared.candelaria at intel.com>
Cc: "Bloomfield, Jon" <jon.bloomfield at intel.com>
Cc: <stable at vger.kernel.org> # v4.9+
---
The alternative would be to use u32 throughout, but that would also mean
keeping the min_t(u32, ...). unsigned long decouples the mechanism from
the API limits, so long as we remember to enforce that the mechanism
copes with the entire range of the API.
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c |  7 +++++--
 drivers/gpu/drm/i915/i915_cmd_parser.c         | 10 +++++-----
 drivers/gpu/drm/i915/i915_drv.h                |  4 ++--
 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 5509946f1a1d..4b09bcd70cf4 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -2267,8 +2267,8 @@ struct eb_parse_work {
 	struct i915_vma *batch;
 	struct i915_vma *shadow;
 	struct i915_vma *trampoline;
-	unsigned int batch_offset;
-	unsigned int batch_length;
+	unsigned long batch_offset;
+	unsigned long batch_length;
 };
 
 static int __eb_parse(struct dma_fence_work *work)
@@ -2338,6 +2338,9 @@ static int eb_parse_pipeline(struct i915_execbuffer *eb,
 	struct eb_parse_work *pw;
 	int err;
 
+	GEM_BUG_ON(overflows_type(eb->batch_start_offset, pw->batch_offset));
+	GEM_BUG_ON(overflows_type(eb->batch_len, pw->batch_length));
+
 	pw = kzalloc(sizeof(*pw), GFP_KERNEL);
 	if (!pw)
 		return -ENOMEM;
diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
index 5ac4a999f05a..e88970256e8e 100644
--- a/drivers/gpu/drm/i915/i915_cmd_parser.c
+++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
@@ -1136,7 +1136,7 @@ find_reg(const struct intel_engine_cs *engine, u32 addr)
 /* Returns a vmap'd pointer to dst_obj, which the caller must unmap */
 static u32 *copy_batch(struct drm_i915_gem_object *dst_obj,
 		       struct drm_i915_gem_object *src_obj,
-		       u32 offset, u32 length)
+		       unsigned long offset, unsigned long length)
 {
 	bool needs_clflush;
 	void *dst, *src;
@@ -1166,8 +1166,8 @@ static u32 *copy_batch(struct drm_i915_gem_object *dst_obj,
 		}
 	}
 	if (IS_ERR(src)) {
+		unsigned long x, n;
 		void *ptr;
-		int x, n;
 
 		/*
 		 * We can avoid clflushing partial cachelines before the write
@@ -1184,7 +1184,7 @@ static u32 *copy_batch(struct drm_i915_gem_object *dst_obj,
 		ptr = dst;
 		x = offset_in_page(offset);
 		for (n = offset >> PAGE_SHIFT; length; n++) {
-			int len = min_t(int, length, PAGE_SIZE - x);
+			int len = min(length, PAGE_SIZE - x);
 
 			src = kmap_atomic(i915_gem_object_get_page(src_obj, n));
 			if (needs_clflush)
@@ -1414,8 +1414,8 @@ static bool shadow_needs_clflush(struct drm_i915_gem_object *obj)
  */
 int intel_engine_cmd_parser(struct intel_engine_cs *engine,
 			    struct i915_vma *batch,
-			    u32 batch_offset,
-			    u32 batch_length,
+			    unsigned long batch_offset,
+			    unsigned long batch_length,
 			    struct i915_vma *shadow,
 			    bool trampoline)
 {
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 72a9449b674e..eef9a821c49c 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1949,8 +1949,8 @@ void intel_engine_init_cmd_parser(struct intel_engine_cs *engine);
 void intel_engine_cleanup_cmd_parser(struct intel_engine_cs *engine);
 int intel_engine_cmd_parser(struct intel_engine_cs *engine,
 			    struct i915_vma *batch,
-			    u32 batch_offset,
-			    u32 batch_length,
+			    unsigned long batch_offset,
+			    unsigned long batch_length,
 			    struct i915_vma *shadow,
 			    bool trampoline);
 #define I915_CMD_PARSER_TRAMPOLINE_SIZE 8
-- 
2.20.1