Re: [Intel-gfx] [PATCH 1/5] drm/i915: Do not define vma on stack

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Sep 14, 2021 at 10:05:03PM +0200, Daniel Vetter wrote:
> On Tue, Sep 14, 2021 at 08:36:56AM -0700, Matthew Brost wrote:
> > On Tue, Sep 14, 2021 at 03:04:59PM +1000, Dave Airlie wrote:
> > > On Tue, 14 Sept 2021 at 14:55, Matthew Brost <matthew.brost@intel.com> wrote:
> > > >
> > > > From: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
> > > >
> > > > Defining vma on stack can cause stack overflow, if
> > > > vma gets populated with new fields.
> > > 
> > > Is there some higher level locking stopping that from getting trashed?
> > > or a guarantee that uc_fw_bind_ggtt is only entered by one thread at a
> > > time?
> > > 
> > 
> > I believe this function is only called during driver load (inherently
> > one thread) or during a GT reset (protected by reset mutex) so at most 1
> > thread can be executing this code at once, thus it is safe to use a
> > global dummy vma in this function.
> 
> This kind of stuff must be documented in kerneldoc comments. Please use
> the inline struct member format.
> 

Forgot to include kerneldoc for this new field, will add.

> Also please document the other fields in that struct, cant hurt :-)

I'll see what I can do but I didn't write this code and may not fully
understand all the fields off hand.

Matt

> -Daniel
> 
> > 
> > Matt
> > 
> > > Dave.
> > > 
> > > >
> > > > Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> > > > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > > > Signed-off-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
> > > > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > > > Reviewed-by: Matthew Brost <matthew.brost@intel.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c | 18 +++++++++---------
> > > >  drivers/gpu/drm/i915/gt/uc/intel_uc_fw.h |  2 ++
> > > >  2 files changed, 11 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> > > > index 3a16d08608a5..f632dbd32b42 100644
> > > > --- a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> > > > +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c
> > > > @@ -413,20 +413,20 @@ static void uc_fw_bind_ggtt(struct intel_uc_fw *uc_fw)
> > > >  {
> > > >         struct drm_i915_gem_object *obj = uc_fw->obj;
> > > >         struct i915_ggtt *ggtt = __uc_fw_to_gt(uc_fw)->ggtt;
> > > > -       struct i915_vma dummy = {
> > > > -               .node.start = uc_fw_ggtt_offset(uc_fw),
> > > > -               .node.size = obj->base.size,
> > > > -               .pages = obj->mm.pages,
> > > > -               .vm = &ggtt->vm,
> > > > -       };
> > > > +       struct i915_vma *dummy = &uc_fw->dummy;
> > > > +
> > > > +       dummy->node.start = uc_fw_ggtt_offset(uc_fw);
> > > > +       dummy->node.size = obj->base.size;
> > > > +       dummy->pages = obj->mm.pages;
> > > > +       dummy->vm = &ggtt->vm;
> > > >
> > > >         GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
> > > > -       GEM_BUG_ON(dummy.node.size > ggtt->uc_fw.size);
> > > > +       GEM_BUG_ON(dummy->node.size > ggtt->uc_fw.size);
> > > >
> > > >         /* uc_fw->obj cache domains were not controlled across suspend */
> > > > -       drm_clflush_sg(dummy.pages);
> > > > +       drm_clflush_sg(dummy->pages);
> > > >
> > > > -       ggtt->vm.insert_entries(&ggtt->vm, &dummy, I915_CACHE_NONE, 0);
> > > > +       ggtt->vm.insert_entries(&ggtt->vm, dummy, I915_CACHE_NONE, 0);
> > > >  }
> > > >
> > > >  static void uc_fw_unbind_ggtt(struct intel_uc_fw *uc_fw)
> > > > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.h b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.h
> > > > index 99bb1fe1af66..693cc0ebcd63 100644
> > > > --- a/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.h
> > > > +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc_fw.h
> > > > @@ -10,6 +10,7 @@
> > > >  #include "intel_uc_fw_abi.h"
> > > >  #include "intel_device_info.h"
> > > >  #include "i915_gem.h"
> > > > +#include "i915_vma.h"
> > > >
> > > >  struct drm_printer;
> > > >  struct drm_i915_private;
> > > > @@ -75,6 +76,7 @@ struct intel_uc_fw {
> > > >         bool user_overridden;
> > > >         size_t size;
> > > >         struct drm_i915_gem_object *obj;
> > > > +       struct i915_vma dummy;
> > > >
> > > >         /*
> > > >          * The firmware build process will generate a version header file with major and
> > > > --
> > > > 2.32.0
> > > >
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch