Re: [Intel-gfx] [PATCH 2/3] drm/i915/selftests: Fix memory corruption in live_lrc_isolation

[Daniel Vetter <daniel@ffwll.ch>]

On Sun, Aug 08, 2021 at 11:07:56AM -0700, Matthew Brost wrote:
> GuC submission has exposed an existing memory corruption in
> live_lrc_isolation. We believe that some writes to the watchdog offsets
> in the LRC (0x178 & 0x17c) can result in trashing of portions of the
> address space. With GuC submission there are additional objects which
> can move the context redzone into the space that is trashed. To
> workaround this avoid poisoning the watchdog.

A Bspec reference here would be good (we can quote anything that's marked
for public release, so doesn't have one of the IP markers).

Also I think the above should be replicated in condensed form instead of
the XXX comment.

With those: Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> since I
definitely have enough clue here for a detailed review.
-Daniel

> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/selftest_lrc.c | 29 +++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> index b0977a3b699b..6500e9fce8a0 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> @@ -1074,6 +1074,32 @@ record_registers(struct intel_context *ce,
>  	goto err_after;
>  }
>  
> +static u32 safe_offset(u32 offset, u32 reg)
> +{
> +	/* XXX skip testing of watchdog */
> +	if (offset == 0x178 || offset == 0x17c)
> +		reg = 0;
> +
> +	return reg;
> +}
> +
> +static int get_offset_mask(struct intel_engine_cs *engine)
> +{
> +	if (GRAPHICS_VER(engine->i915) < 12)
> +		return 0xfff;
> +
> +	switch (engine->class) {
> +	default:
> +	case RENDER_CLASS:
> +		return 0x07ff;
> +	case COPY_ENGINE_CLASS:
> +		return 0x0fff;
> +	case VIDEO_DECODE_CLASS:
> +	case VIDEO_ENHANCEMENT_CLASS:
> +		return 0x3fff;
> +	}
> +}
> +
>  static struct i915_vma *load_context(struct intel_context *ce, u32 poison)
>  {
>  	struct i915_vma *batch;
> @@ -1117,7 +1143,8 @@ static struct i915_vma *load_context(struct intel_context *ce, u32 poison)
>  		len = (len + 1) / 2;
>  		*cs++ = MI_LOAD_REGISTER_IMM(len);
>  		while (len--) {
> -			*cs++ = hw[dw];
> +			*cs++ = safe_offset(hw[dw] & get_offset_mask(ce->engine),
> +					    hw[dw]);
>  			*cs++ = poison;
>  			dw += 2;
>  		}
> -- 
> 2.28.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch