Re: [Intel-gfx] [PATCH 07/11] drm/i915: Add i915_gem_context_is_full_ppgtt

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 02/09/2021 15:20, Daniel Vetter wrote:
> And use it anywhere we have open-coded checks for ctx->vm that really
> only check for full ppgtt.
> 
> Plus for paranoia add a GEM_BUG_ON that checks it's really only set
> when we have full ppgtt, just in case. gem_context->vm is different
> since it's NULL in ggtt mode, unlike intel_context->vm or gt->vm,
> which is always set.
> 
> v2: 0day found a testcase that I missed.
> 
> Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jon Bloomfield <jon.bloomfield@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Jason Ekstrand <jason@jlekstrand.net>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_context.c           | 2 +-
>   drivers/gpu/drm/i915/gem/i915_gem_context.h           | 7 +++++++
>   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c        | 2 +-
>   drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c | 6 +++---
>   4 files changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index 7a566fb7cca4..1eec85944c1f 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -1566,7 +1566,7 @@ static int get_ppgtt(struct drm_i915_file_private *file_priv,
>   	int err;
>   	u32 id;
>   
> -	if (!rcu_access_pointer(ctx->vm))
> +	if (!i915_gem_context_is_full_ppgtt(ctx))

It reads a bit wrong because GEM context cannot *be* full ppggt. It can 
be associated with a VM which is or isn't full ppgtt. So a test on a VM 
retrieved from a context is semnntically more correct. Perhaps you want 
to consider adding a helper to that effect instead? It could mean 
splitting into two helpers (getter + test) or maybe just renaming would 
work. Like i915_gem_context_has_full_ppgtt_vm(ctx)?

Regards,

Tvrtko

>   		return -ENODEV;
>   
>   	rcu_read_lock();
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.h b/drivers/gpu/drm/i915/gem/i915_gem_context.h
> index da6e8b506d96..37536a260e6e 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.h
> @@ -154,6 +154,13 @@ i915_gem_context_vm(struct i915_gem_context *ctx)
>   	return rcu_dereference_protected(ctx->vm, lockdep_is_held(&ctx->mutex));
>   }
>   
> +static inline bool i915_gem_context_is_full_ppgtt(struct i915_gem_context *ctx)
> +{
> +	GEM_BUG_ON(!!rcu_access_pointer(ctx->vm) != HAS_FULL_PPGTT(ctx->i915));
> +
> +	return !!rcu_access_pointer(ctx->vm);
> +}
> +
>   static inline struct i915_address_space *
>   i915_gem_context_get_eb_vm(struct i915_gem_context *ctx)
>   {
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 905b1cbd22d5..40f08948f0b2 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -749,7 +749,7 @@ static int eb_select_context(struct i915_execbuffer *eb)
>   		return PTR_ERR(ctx);
>   
>   	eb->gem_context = ctx;
> -	if (rcu_access_pointer(ctx->vm))
> +	if (i915_gem_context_is_full_ppgtt(ctx))
>   		eb->invalid_flags |= EXEC_OBJECT_NEEDS_GTT;
>   
>   	return 0;
> diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
> index fc7fb33a3a52..947154e445a7 100644
> --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
> @@ -704,7 +704,7 @@ static int igt_ctx_exec(void *arg)
>   				pr_err("Failed to fill dword %lu [%lu/%lu] with gpu (%s) [full-ppgtt? %s], err=%d\n",
>   				       ndwords, dw, max_dwords(obj),
>   				       engine->name,
> -				       yesno(!!rcu_access_pointer(ctx->vm)),
> +				       yesno(i915_gem_context_is_full_ppgtt(ctx)),
>   				       err);
>   				intel_context_put(ce);
>   				kernel_context_close(ctx);
> @@ -838,7 +838,7 @@ static int igt_shared_ctx_exec(void *arg)
>   				pr_err("Failed to fill dword %lu [%lu/%lu] with gpu (%s) [full-ppgtt? %s], err=%d\n",
>   				       ndwords, dw, max_dwords(obj),
>   				       engine->name,
> -				       yesno(!!rcu_access_pointer(ctx->vm)),
> +				       yesno(i915_gem_context_is_full_ppgtt(ctx)),
>   				       err);
>   				intel_context_put(ce);
>   				kernel_context_close(ctx);
> @@ -1417,7 +1417,7 @@ static int igt_ctx_readonly(void *arg)
>   				pr_err("Failed to fill dword %lu [%lu/%lu] with gpu (%s) [full-ppgtt? %s], err=%d\n",
>   				       ndwords, dw, max_dwords(obj),
>   				       ce->engine->name,
> -				       yesno(!!ctx_vm(ctx)),
> +				       yesno(i915_gem_context_is_full_ppgtt(ctx)),
>   				       err);
>   				i915_gem_context_unlock_engines(ctx);
>   				goto out_file;
>