On 2021-12-02 at 14:54:23 +0530, Tejas Upadhyay wrote: > From: Chris Wilson <[email protected]> > > Introduce the concept of padding the i915_vma with guard pages before > and aft. The major consequence is that all ordinary uses of i915_vma > must use i915_vma_offset/i915_vma_size and not i915_vma.node.start/size > directly, as the drm_mm_node will include the guard pages that surround > our object. > > The biggest connundrum is how exactly to mix requesting a fixed address > with guard pages, particularly through the existing uABI. The user does > not know about guard pages, so such must be transparent to the user, and > so the execobj.offset must be that of the object itself excluding the > guard. So a PIN_OFFSET_FIXED must then be exclusive of the guard pages. > The caveat is that some placements will be impossible with guard pages, > as wrap arounds need to be avoided, and the vma itself will require a > larger node. We must we not report EINVAL but ENOSPC as these are > unavailable locations within the GTT rather than conflicting user > requirements. > > In the next patch, we start using guard pages for scanout objects. While > these are limited to GGTT vma, on a few platforms these vma (or at least > an alias of the vma) is shared with userspace, so we may leak the > existence of such guards if we are not careful to ensure that the > execobj.offset is transparent and excludes the guards. (On such platforms > like ivb, without full-ppgtt, userspace has to use relocations so the > presence of more untouchable regions within its GTT such be of no further > issue.) > > v2: Include the guard range in the overflow checks and placement > restrictions. > > v3: Fix the check on the placement upper bound. The request user offset > is relative to the guard offset (not the node.start) and so we should > not include the initial guard offset again when computing the upper > bound of the node. Commit subject says v2 but we have teh change log for v3.
Patch looks good to me. Reviewed-by: Ramalingam C <[email protected]> > > Signed-off-by: Chris Wilson <[email protected]> > Cc: Matthew Auld <[email protected]> > Reviewed-by: Matthew Auld <[email protected]> > Signed-off-by: Tejas Upadhyay <[email protected]> > --- > drivers/gpu/drm/i915/gt/intel_ggtt.c | 12 ++++++++++-- > drivers/gpu/drm/i915/i915_vma.c | 26 +++++++++++++++++++++----- > drivers/gpu/drm/i915/i915_vma.h | 5 +++-- > drivers/gpu/drm/i915/i915_vma_types.h | 3 ++- > 4 files changed, 36 insertions(+), 10 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c > b/drivers/gpu/drm/i915/gt/intel_ggtt.c > index 07133f0c529e..282ed6dd3ca2 100644 > --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c > +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c > @@ -256,8 +256,12 @@ static void gen8_ggtt_insert_entries(struct > i915_address_space *vm, > > gte = (gen8_pte_t __iomem *)ggtt->gsm; > gte += vma->node.start / I915_GTT_PAGE_SIZE; > - end = gte + vma->node.size / I915_GTT_PAGE_SIZE; > > + end = gte + vma->guard / I915_GTT_PAGE_SIZE; > + while (gte < end) > + gen8_set_pte(gte++, vm->scratch[0]->encode); > + > + end += (vma->node.size - vma->guard) / I915_GTT_PAGE_SIZE; > for_each_sgt_daddr(addr, iter, vma->pages) > gen8_set_pte(gte++, pte_encode | addr); > GEM_BUG_ON(gte > end); > @@ -307,8 +311,12 @@ static void gen6_ggtt_insert_entries(struct > i915_address_space *vm, > > gte = (gen6_pte_t __iomem *)ggtt->gsm; > gte += vma->node.start / I915_GTT_PAGE_SIZE; > - end = gte + vma->node.size / I915_GTT_PAGE_SIZE; > > + end = gte + vma->guard / I915_GTT_PAGE_SIZE; > + while (gte < end) > + gen8_set_pte(gte++, vm->scratch[0]->encode); > + > + end += (vma->node.size - vma->guard) / I915_GTT_PAGE_SIZE; > for_each_sgt_daddr(addr, iter, vma->pages) > iowrite32(vm->pte_encode(addr, level, flags), gte++); > GEM_BUG_ON(gte > end); > diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c > index 10473ce8a047..080ffa583edf 100644 > --- a/drivers/gpu/drm/i915/i915_vma.c > +++ b/drivers/gpu/drm/i915/i915_vma.c > @@ -658,7 +658,7 @@ bool i915_gem_valid_gtt_space(struct i915_vma *vma, > unsigned long color) > static int > i915_vma_insert(struct i915_vma *vma, u64 size, u64 alignment, u64 flags) > { > - unsigned long color; > + unsigned long color, guard; > u64 start, end; > int ret; > > @@ -666,7 +666,7 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 > alignment, u64 flags) > GEM_BUG_ON(drm_mm_node_allocated(&vma->node)); > > size = max(size, vma->size); > - alignment = max(alignment, vma->display_alignment); > + alignment = max_t(typeof(alignment), alignment, vma->display_alignment); > if (flags & PIN_MAPPABLE) { > size = max_t(typeof(size), size, vma->fence_size); > alignment = max_t(typeof(alignment), > @@ -677,6 +677,9 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 > alignment, u64 flags) > GEM_BUG_ON(!IS_ALIGNED(alignment, I915_GTT_MIN_ALIGNMENT)); > GEM_BUG_ON(!is_power_of_2(alignment)); > > + guard = vma->guard; /* retain guard across rebinds */ > + guard = ALIGN(guard, alignment); > + > start = flags & PIN_OFFSET_BIAS ? flags & PIN_OFFSET_MASK : 0; > GEM_BUG_ON(!IS_ALIGNED(start, I915_GTT_PAGE_SIZE)); > > @@ -686,12 +689,13 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 > alignment, u64 flags) > if (flags & PIN_ZONE_4G) > end = min_t(u64, end, (1ULL << 32) - I915_GTT_PAGE_SIZE); > GEM_BUG_ON(!IS_ALIGNED(end, I915_GTT_PAGE_SIZE)); > + GEM_BUG_ON(2 * guard > end); > > /* If binding the object/GGTT view requires more space than the entire > * aperture has, reject it early before evicting everything in a vain > * attempt to find space. > */ > - if (size > end) { > + if (size > end - 2 * guard) { > DRM_DEBUG("Attempting to bind an object larger than the > aperture: request=%llu > %s aperture=%llu\n", > size, flags & PIN_MAPPABLE ? "mappable" : "total", > end); > @@ -707,13 +711,24 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 > alignment, u64 flags) > if (!IS_ALIGNED(offset, alignment) || > range_overflows(offset, size, end)) > return -EINVAL; > + /* > + * The caller knows not of the guard added by others and > + * requests for the offset of the start of its buffer > + * to be fixed, which may not be the same as the position > + * of the vma->node due to the guard pages. > + */ > + if (offset < guard || offset + size > end - guard) > + return -ENOSPC; > + > > ret = i915_gem_gtt_reserve(vma->vm, &vma->node, > - size, offset, color, > - flags); > + size + 2 * guard, > + offset - guard, > + color, flags); > if (ret) > return ret; > } else { > + size += 2 * guard; > /* > * We only support huge gtt pages through the 48b PPGTT, > * however we also don't want to force any alignment for > @@ -760,6 +775,7 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 > alignment, u64 flags) > GEM_BUG_ON(!i915_gem_valid_gtt_space(vma, color)); > > list_add_tail(&vma->vm_link, &vma->vm->bound_list); > + vma->guard = guard; > > return 0; > } > diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h > index 1d13d619ff86..d35ce4e7170c 100644 > --- a/drivers/gpu/drm/i915/i915_vma.h > +++ b/drivers/gpu/drm/i915/i915_vma.h > @@ -128,12 +128,13 @@ static inline bool i915_vma_is_closed(const struct > i915_vma *vma) > static inline u64 i915_vma_size(const struct i915_vma *vma) > { > GEM_BUG_ON(!drm_mm_node_allocated(&vma->node)); > - return vma->node.size; > + return vma->node.size - 2 * vma->guard; > } > > static inline u64 __i915_vma_offset(const struct i915_vma *vma) > { > - return vma->node.start; > + /* The actual start of the vma->pages is after the guard pages. */ > + return vma->node.start + vma->guard; > } > > static inline u64 i915_vma_offset(const struct i915_vma *vma) > diff --git a/drivers/gpu/drm/i915/i915_vma_types.h > b/drivers/gpu/drm/i915/i915_vma_types.h > index f03fa96a1701..a224daf1044e 100644 > --- a/drivers/gpu/drm/i915/i915_vma_types.h > +++ b/drivers/gpu/drm/i915/i915_vma_types.h > @@ -195,14 +195,15 @@ struct i915_vma { > struct i915_fence_reg *fence; > > u64 size; > - u64 display_alignment; > struct i915_page_sizes page_sizes; > > /* mmap-offset associated with fencing for this vma */ > struct i915_mmap_offset *mmo; > > + u32 guard; /* padding allocated around vma->pages within the node */ > u32 fence_size; > u32 fence_alignment; > + u32 display_alignment; > > /** > * Count of the number of times this vma has been opened by different > -- > 2.31.1 >
