Re: [PATCH 2/2] drm/i915/gtt: Avoid using addresses in non-canonical form.

Michel Thierry
2015-09-15T14:01:28Z

On 9/15/2015 2:30 PM, Michał Winiarski wrote:
> According to bspec, some parts of HW expect the addresses to be in
> a canonical form where bits [63:48] == [47]. Lets satisfy the HW by
> converting the address prior to allocating/clearing the entries in page
> tables.

Thanks for sending this. A couple of comments below.
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 7ff7239..f25a33f 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -766,6 +766,7 @@ static void gen8_ppgtt_clear_range(struct i915_address_space *vm,
> } else {
> uint64_t templ4, pml4e;
> struct i915_page_directory_pointer *pdp;
> + start = gen8_canonical_addr(start);
>
> gen8_for_each_pml4e(pdp, &ppgtt->pml4, start, length, templ4, pml4e) {
> gen8_ppgtt_clear_pte_range(vm, pdp, start, length,
> @@ -1227,15 +1228,10 @@ static int gen8_alloc_va_range_3lvl(struct i915_address_space *vm,
> uint32_t pdpes = I915_PDPES_PER_PDP(dev);
> int ret;
>
> - /* Wrap is never okay since we can only represent 48b, and we don't
> - * actually use the other side of the canonical address space.
> - */
> + /* Wrap is never okay */
> if (WARN_ON(start + length < start))
> return -ENODEV;

start can be in canonical form here (alloc_va_range_4lvl calls
alloc_va_range_3lvl), and then this check could fail, e.g: first alloc
when using top-down.
Just move it to gen8_alloc_va_range like you did to the check below.

>
> - if (WARN_ON(start + length > vm->total))
> - return -ENODEV;
> -
> ret = alloc_gen8_temp_bitmaps(&new_page_dirs, &new_page_tables, pdpes);
> if (ret)
> return ret;
> @@ -1333,6 +1329,8 @@ static int gen8_alloc_va_range_4lvl(struct i915_address_space *vm,
> uint64_t temp, pml4e;
> int ret = 0;
>
> + start = gen8_canonical_addr(start);
> +

Can you move this to gen8_alloc_va_range (48bit path) instead?
That will keep it in sync to _clear_range.

Also, I know it isn't really required in gen8_ppgtt_insert_entries (as
it only relies in pdp/pdp/pt indexes), but it will be nice to have
alloc/insert/clear functions in sync.

> /* Do the pml4 allocations first, so we don't need to track the newly
> * allocated tables below the pdp */
> bitmap_zero(new_pdps, GEN8_PML4ES_PER_PML4);
> @@ -1377,6 +1375,9 @@ static int gen8_alloc_va_range(struct i915_address_space *vm,
> struct i915_hw_ppgtt *ppgtt =
> container_of(vm, struct i915_hw_ppgtt, base);
>
> + if (WARN_ON(start + length > vm->total))
> + return -ENODEV;
> +
> if (USES_FULL_48BIT_PPGTT(vm->dev))
> return gen8_alloc_va_range_4lvl(vm, &ppgtt->pml4, start, length);
> else
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
> index 8275007..9397387 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.h
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
> @@ -503,6 +503,11 @@ static inline size_t gen8_pte_count(uint64_t address, uint64_t length)
> return i915_pte_count(address, length, GEN8_PDE_SHIFT);
> }
>
> +static inline uint64_t gen8_canonical_addr(uint64_t address)

Feel free to ignore this one, but this isn't gen8 per se, so I vote for
to_canonical_addr().

> +{
> + return ((int64_t)address << 16) >> 16;
> +}
> +
> static inline dma_addr_t
> i915_page_dir_dma_addr(const struct i915_hw_ppgtt *ppgtt, const unsigned n)
> {