[Intel-gfx] [PATCH 1/3] drm/i915/gt: Do not allow setting ring size for legacy ring submission

[Tvrtko Ursulin]

I had some questions on the trybot mailing list, let me copy&paste..

On 21/06/2021 12:41, Maarten Lankhorst wrote:
> It doesn't work for legacy ring submission, and is in the best case
> ignored.

Looks rejected instead of ignored:

static int set_ringsize(struct i915_gem_context *ctx,
             struct drm_i915_gem_context_param *args)
{
     if (!HAS_LOGICAL_RING_CONTEXTS(ctx->i915))
         return -ENODEV;
> 
> In the worst case we end up freeing engine->legacy.ring for all other
> active engines, resulting in a use-after-free.

Worst case is cloning because ring_context_alloc is not taking a 
reference to engine->legacy.ring, or something else?

Regards,

Tvrtko

> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Fixes: 88be76cdafc7 ("drm/i915: Allow userspace to specify ringsize on construction")
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/gt/intel_context_param.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_param.c b/drivers/gpu/drm/i915/gt/intel_context_param.c
> index 65dcd090245d..412c36d1b1dd 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_param.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context_param.c
> @@ -12,6 +12,9 @@ int intel_context_set_ring_size(struct intel_context *ce, long sz)
>   {
>   	int err;
>   
> +	if (ce->engine->gt->submission_method == INTEL_SUBMISSION_RING)
> +		return 0;
> +
>   	if (intel_context_lock_pinned(ce))
>   		return -EINTR;
>   
>