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

[Daniel Vetter]

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 at intel.com> wrote:
> > >
> > > From: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota at 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.

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

> 
> Matt
> 
> > Dave.
> > 
> > >
> > > Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> > > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > > Signed-off-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota at intel.com>
> > > Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> > > Reviewed-by: Matthew Brost <matthew.brost at 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