Re: [PATCH] drm/i915: Do not drop pagetables when empty

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 14 Jun 2017, Eric Blau <eblau@eblau.com> wrote:
> Can the following patch please be included in the next stable release?
> It looks like it was submitted previously by Daniel Vetter, but has not
> been included in 4.11.y yet. Thanks.

The previous submission would be [1]. Please reference that instead of
resending patches with incomplete upstream references. Thank you.

BR,
Jani.


[1] http://mid.mail-archive.com/20170526082906.8982-1-daniel.vetter@ffwll.ch

> From 64b1d89f358df34701d92471b65f99f4eff1b384 Mon Sep 17 00:00:00 2001
> From: Chris Wilson <chris@chris-wilson.co.uk>
> Date: Thu, 18 May 2017 11:00:15 +0100
> Subject: [PATCH] drm/i915: Do not drop pagetables when empty
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
>
> Due to a race with the shrinker, when we try to allocate a pagetable, we
> may end up shrinking it instead. This comes as a nasty surprise as we
> try to dereference it to fill in the pagetable entries for the object.
>
> In linus/master this is fixed by pinning the pagetables prior to
> allocation, but that backport is roughly
>  drivers/gpu/drm/i915/i915_debugfs.c   |    2 +-
>  drivers/gpu/drm/i915/i915_gem_evict.c |   12 +-
>  drivers/gpu/drm/i915/i915_gem_gtt.c   | 2017 ++++++++++++++-------------------
>  drivers/gpu/drm/i915/i915_gem_gtt.h   |  123 +-
>  drivers/gpu/drm/i915/i915_trace.h     |  104 --
>  drivers/gpu/drm/i915/i915_vgpu.c      |    9 +-
>  drivers/gpu/drm/i915/i915_vma.c       |    9 -
>  drivers/gpu/drm/i915/intel_lrc.c      |    4 +-
>  8 files changed, 946 insertions(+), 1334 deletions(-)
> i.e. unsuitable for stable. Instead we neuter the code that tried to
> free the pagetables.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99295
> Fixes: 2ce5179fe826 ("drm/i915/gtt: Free unused lower-level page tables")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Michel Thierry <michel.thierry@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Michał Winiarski <michal.winiarski@intel.com>
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: intel-gfx@lists.freedesktop.org
> Cc: <stable@vger.kernel.org> # v4.10+
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 10 ----------
>  1 file changed, 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 96e45a4d5441..4f581adf2fcf 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -755,10 +755,6 @@ static bool gen8_ppgtt_clear_pt(struct i915_address_space *vm,
>  	GEM_BUG_ON(pte_end > GEN8_PTES);
>  
>  	bitmap_clear(pt->used_ptes, pte, num_entries);
> -	if (USES_FULL_PPGTT(vm->i915)) {
> -		if (bitmap_empty(pt->used_ptes, GEN8_PTES))
> -			return true;
> -	}
>  
>  	pt_vaddr = kmap_px(pt);
>  
> @@ -798,9 +794,6 @@ static bool gen8_ppgtt_clear_pd(struct i915_address_space *vm,
>  		}
>  	}
>  
> -	if (bitmap_empty(pd->used_pdes, I915_PDES))
> -		return true;
> -
>  	return false;
>  }
>  
> @@ -829,9 +822,6 @@ static bool gen8_ppgtt_clear_pdp(struct i915_address_space *vm,
>  
>  	mark_tlbs_dirty(ppgtt);
>  
> -	if (bitmap_empty(pdp->used_pdpes, I915_PDPES_PER_PDP(dev_priv)))
> -		return true;
> -
>  	return false;
>  }
>  
>

-- 
Jani Nikula, Intel Open Source Technology Center
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