Re: [Intel-gfx] [PATCH 2/3] drm/i915/selftests: Fix memory corruption in live_lrc_isolation

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Aug 09, 2021 at 07:37:39PM +0000, Matthew Brost wrote:
> On Mon, Aug 09, 2021 at 03:38:38PM +0200, Daniel Vetter wrote:
> > On Sun, Aug 08, 2021 at 11:07:56AM -0700, Matthew Brost wrote:
> > > GuC submission has exposed an existing memory corruption in
> > > live_lrc_isolation. We believe that some writes to the watchdog offsets
> > > in the LRC (0x178 & 0x17c) can result in trashing of portions of the
> > > address space. With GuC submission there are additional objects which
> > > can move the context redzone into the space that is trashed. To
> > > workaround this avoid poisoning the watchdog.
> > 
> > A Bspec reference here would be good (we can quote anything that's marked
> > for public release, so doesn't have one of the IP markers).
> >
> 
> Let me see what I dig up in the bspec.
> 
> BTW - Hopefully we can root cause this soon with a proper fix.

Well if it's work-in-progress duct-tape without reference that's fine
too, then perhaps sprinkle a JIRA number here (just not the full link,
intel IT doesn't like those leaking). Just something that in a few months
when someone reads that code they can stitch together the story again.
-Daniel

>  
> > Also I think the above should be replicated in condensed form instead of
> > the XXX comment.
> >
> 
> Sure.
> 
> Matt
> 
> > With those: Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> since I
> > definitely have enough clue here for a detailed review.
> > -Daniel
> > 
> > > 
> > > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/gt/selftest_lrc.c | 29 +++++++++++++++++++++++++-
> > >  1 file changed, 28 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> > > index b0977a3b699b..6500e9fce8a0 100644
> > > --- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> > > +++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> > > @@ -1074,6 +1074,32 @@ record_registers(struct intel_context *ce,
> > >  	goto err_after;
> > >  }
> > >  
> > > +static u32 safe_offset(u32 offset, u32 reg)
> > > +{
> > > +	/* XXX skip testing of watchdog */
> > > +	if (offset == 0x178 || offset == 0x17c)
> > > +		reg = 0;
> > > +
> > > +	return reg;
> > > +}
> > > +
> > > +static int get_offset_mask(struct intel_engine_cs *engine)
> > > +{
> > > +	if (GRAPHICS_VER(engine->i915) < 12)
> > > +		return 0xfff;
> > > +
> > > +	switch (engine->class) {
> > > +	default:
> > > +	case RENDER_CLASS:
> > > +		return 0x07ff;
> > > +	case COPY_ENGINE_CLASS:
> > > +		return 0x0fff;
> > > +	case VIDEO_DECODE_CLASS:
> > > +	case VIDEO_ENHANCEMENT_CLASS:
> > > +		return 0x3fff;
> > > +	}
> > > +}
> > > +
> > >  static struct i915_vma *load_context(struct intel_context *ce, u32 poison)
> > >  {
> > >  	struct i915_vma *batch;
> > > @@ -1117,7 +1143,8 @@ static struct i915_vma *load_context(struct intel_context *ce, u32 poison)
> > >  		len = (len + 1) / 2;
> > >  		*cs++ = MI_LOAD_REGISTER_IMM(len);
> > >  		while (len--) {
> > > -			*cs++ = hw[dw];
> > > +			*cs++ = safe_offset(hw[dw] & get_offset_mask(ce->engine),
> > > +					    hw[dw]);
> > >  			*cs++ = poison;
> > >  			dw += 2;
> > >  		}
> > > -- 
> > > 2.28.0
> > > 
> > 
> > -- 
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch

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