Fixes a crash I see on Broadwell.

Tested-by: Alex Smith <asm...@feralinteractive.com>

Cc to stable for 18.2? The crash is reproducible there as well.

On Tue, 2 Oct 2018 at 23:25, Jason Ekstrand <ja...@jlekstrand.net> wrote:

> Previously, we just went ahead and emitted MI_BATCH_BUFFER_START as
> normal.  If we are near enough to the end, this can cause us to start a
> new BO just for the MI_BATCH_BUFFER_START which messes up chaining.  We
> always reserve enough space at the end for an MI_BATCH_BUFFER_START so
> we can just increment cmd_buffer->batch.end prior to emitting the
> command.
>
> Fixes: a0b133286a3 "anv/batch_chain: Simplify secondary batch return..."
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107926
> ---
>  src/intel/vulkan/anv_batch_chain.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/src/intel/vulkan/anv_batch_chain.c
> b/src/intel/vulkan/anv_batch_chain.c
> index 3e13553ac18..e08e07ad7bd 100644
> --- a/src/intel/vulkan/anv_batch_chain.c
> +++ b/src/intel/vulkan/anv_batch_chain.c
> @@ -894,8 +894,17 @@ anv_cmd_buffer_end_batch_buffer(struct anv_cmd_buffer
> *cmd_buffer)
>            * It doesn't matter where it points now so long as has a valid
>            * relocation.  We'll adjust it later as part of the chaining
>            * process.
> +          *
> +          * We set the end of the batch a little short so we would be
> sure we
> +          * have room for the chaining command.  Since we're about to
> emit the
> +          * chaining command, let's set it back where it should go.
>            */
> +         cmd_buffer->batch.end += GEN8_MI_BATCH_BUFFER_START_length * 4;
> +         assert(cmd_buffer->batch.start == batch_bo->bo.map);
> +         assert(cmd_buffer->batch.end == batch_bo->bo.map +
> batch_bo->bo.size);
> +
>           emit_batch_buffer_start(cmd_buffer, &batch_bo->bo, 0);
> +         assert(cmd_buffer->batch.start == batch_bo->bo.map);
>        } else {
>           cmd_buffer->exec_mode = ANV_CMD_BUFFER_EXEC_MODE_COPY_AND_CHAIN;
>        }
> --
> 2.17.1
>
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