Re: [PATCH igt 2/2] lib: Remove illegal instructions from hang injection

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

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

> The idea behind using an illegal instruction was to hang the GPU must
> faster than simply using the recursive batch. However, we stopped doing
> so on gen8+ as the CS parser was much laxer and allowed the illegal
> command through but still interpreted the packet length (jumping over
> the recursive batch buffer start that followed). Sandybridge doesn't
> just hang the GPU when it encounters an illegal command on the BLT
> engine, it hangs the machine. That goes above and beyond testing our
> hangcheck + reset, so remove the deadly instructions.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  lib/igt_gt.c | 25 +++++--------------------
>  1 file changed, 5 insertions(+), 20 deletions(-)
>
> diff --git a/lib/igt_gt.c b/lib/igt_gt.c
> index 6f7daa5e..d5e8b557 100644
> --- a/lib/igt_gt.c
> +++ b/lib/igt_gt.c
> @@ -270,30 +270,15 @@ igt_hang_t igt_hang_ctx(int fd,
>  
>  	memset(b, 0xc5, sizeof(b));
>  
> -	/*
> -	 * We emit invalid command to provoke a gpu hang.
> -	 * If that doesn't work, we do bb start loop.
> -	 * Note that the bb start aligment is illegal due this.
> -	 * But hey, we are here to hang the gpu so whatever works.
> -	 * We skip 0xfffffff on gen9 as it confuses hw in an such a way that
> -	 * it will skip over the bb start, causing runaway head and
> -	 * thus much slower hang detection.
> -	 */

Daydreaming about MI_HALT,

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

>  	len = 2;
> -	if (intel_gen(intel_get_drm_devid(fd)) >= 8) {
> -		b[0] = MI_NOOP;
> +	if (intel_gen(intel_get_drm_devid(fd)) >= 8)
>  		len++;
> -	} else {
> -		b[0] = 0xffffffff;
> -	}
> -
> -	b[1] = MI_BATCH_BUFFER_START | (len - 2);
> -	b[1+len] = MI_BATCH_BUFFER_END;
> -	b[2+len] = MI_NOOP;
> +	b[0] = MI_BATCH_BUFFER_START | (len - 2);
> +	b[len] = MI_BATCH_BUFFER_END;
> +	b[len+1] = MI_NOOP;
>  	gem_write(fd, exec.handle, 0, b, sizeof(b));
>  
> -	reloc.offset = 8;
> -	reloc.delta = 4;
> +	reloc.offset = sizeof(uint32_t);
>  	reloc.target_handle = exec.handle;
>  	reloc.read_domains = I915_GEM_DOMAIN_COMMAND;
>  
> -- 
> 2.13.3
>
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