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

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Sep 02, 2021 at 03:54:36PM +0100, Tvrtko Ursulin wrote:
> 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)?

The pointer isn't set when the driver/context isn't running in full ppgtt
mode. This is why I've added the GEM_BUG_ON to check we're not breaking
any invariants. So yeah it is a full ppgtt context or it's not, that is
indeed the question here.

I'm happy to bikeshed the naming, but I don't see how your suggestion is
an improvement.
-Daniel


> 
> 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;
> > 

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