Re: [PATCH] drm/i915: Avoid mixing integer types during batch copies

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> 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@intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: "Candelaria, Jared" <jared.candelaria@intel.com>
> Cc: "Bloomfield, Jon" <jon.bloomfield@intel.com>
> Cc: <stable@vger.kernel.org> # v4.9+

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> ---
> 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