On Mon, Oct 31, 2016 at 05:24:45PM +0200, Mika Kuoppala wrote:
> Comparing pte index to a number of entries is wrong
> when clearing a range of pte entries. Use end marker
> of 'one past' to correctly point adequate number of
> ptes to the scratch page.
>
> Fixes: d209b9c3cd28 ("drm/i915/gtt: Split gen8_ppgtt_clear_pte_range")
> References: https://bugs.freedesktop.org/show_bug.cgi?id=98282
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Michel Thierry <michel.thierry@xxxxxxxxx>
> Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem_gtt.c | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index e7afad5..cda263c 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -712,13 +712,13 @@ static int gen8_48b_mm_switch(struct i915_hw_ppgtt *ppgtt,
> */
> static bool gen8_ppgtt_clear_pt(struct i915_address_space *vm,
> struct i915_page_table *pt,
> - uint64_t start,
> - uint64_t length)
> + const uint64_t start,
> + const uint64_t length)
> {
> struct i915_hw_ppgtt *ppgtt = i915_vm_to_ppgtt(vm);
> - unsigned int pte_start = gen8_pte_index(start);
> - unsigned int num_entries = gen8_pte_count(start, length);
> - uint64_t pte;
> + const unsigned int num_entries = gen8_pte_count(start, length);
> + unsigned int pte = gen8_pte_index(start);
> + unsigned int pte_end = pte + num_entries;
> gen8_pte_t *pt_vaddr;
> gen8_pte_t scratch_pte = gen8_pte_encode(vm->scratch_page.daddr,
> I915_CACHE_LLC);
> @@ -726,17 +726,20 @@ static bool gen8_ppgtt_clear_pt(struct i915_address_space *vm,
> if (WARN_ON(!px_page(pt)))
> return false;
>
> - bitmap_clear(pt->used_ptes, pte_start, num_entries);
> + bitmap_clear(pt->used_ptes, pte, num_entries);
>
> if (bitmap_empty(pt->used_ptes, GEN8_PTES)) {
> free_pt(vm->dev, pt);
> return true;
> }
>
> + if (WARN_ON_ONCE(pte_end > GEN8_PTES))
> + pte_end = GEN8_PTES;
Internal programming error, if you hit all the upper layers are dead,
i.e. bug on. GEM_BUG_ON.
And the assert should be earlier since you have already used the invalid
values (i.e. pte+num_entries).
> +
> pt_vaddr = kmap_px(pt);
>
> - for (pte = pte_start; pte < num_entries; pte++)
Nice catch.
R-b on this part, less enamoured with the reset.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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