Revert "drm/i915/lmem: Limit block size to 4G"

Mixing I915_ALLOC_CONTIGUOUS and I915_ALLOC_MAX_SEGMENT_SIZE fared
badly. The two directives conflict, with the contiguous request setting
the min_order to the full size of the object, and the max-segment-size
setting the max_order to the limit of the DMA mapper. This results in a
situation where max_order < min_order, causing our sanity checks to
fail.

Instead of limiting the buddy block size, in the previous patch we split
the oversized buddy into multiple scatterlist elements.

Fixes: d2cf0125d4a1 ("drm/i915/lmem: Limit block size to 4G")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201202173444.14903-2-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_region.c b/drivers/gpu/drm/i915/gem/i915_gem_region.c
index 7d05b5f..835bd01 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_region.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_region.c
@@ -43,7 +43,7 @@ i915_gem_object_get_pages_buddy(struct drm_i915_gem_object *obj)
                return -ENOMEM;
        }
 
-       flags = I915_ALLOC_MIN_PAGE_SIZE | I915_ALLOC_MAX_SEGMENT_SIZE;
+       flags = I915_ALLOC_MIN_PAGE_SIZE;
        if (obj->flags & I915_BO_ALLOC_CONTIGUOUS)
                flags |= I915_ALLOC_CONTIGUOUS;
 

diff --git a/drivers/gpu/drm/i915/intel_memory_region.c b/drivers/gpu/drm/i915/intel_memory_region.c
index ae36e2f..b326993 100644 (file)
--- a/drivers/gpu/drm/i915/intel_memory_region.c
+++ b/drivers/gpu/drm/i915/intel_memory_region.c
@@ -72,7 +72,6 @@ __intel_memory_region_get_pages_buddy(struct intel_memory_region *mem,
                                      struct list_head *blocks)
 {
        unsigned int min_order = 0;
-       unsigned int max_order;
        unsigned long n_pages;
 
        GEM_BUG_ON(!IS_ALIGNED(size, mem->mm.chunk_size));
@@ -93,28 +92,13 @@ __intel_memory_region_get_pages_buddy(struct intel_memory_region *mem,
 
        n_pages = size >> ilog2(mem->mm.chunk_size);
 
-       /*
-        * If we going to feed this into an sg list we should limit the block
-        * sizes such that we don't exceed the i915_sg_segment_size().
-        */
-       if (flags & I915_ALLOC_MAX_SEGMENT_SIZE) {
-               unsigned int max_segment = i915_sg_segment_size();
-
-               if (GEM_WARN_ON(max_segment < mem->mm.chunk_size))
-                       max_order = 0;
-               else
-                       max_order = ilog2(max_segment) - ilog2(mem->mm.chunk_size);
-       } else {
-               max_order = mem->mm.max_order;
-       }
-
        mutex_lock(&mem->mm_lock);
 
        do {
                struct i915_buddy_block *block;
                unsigned int order;
 
-               order = min_t(u32, fls(n_pages) - 1, max_order);
+               order = fls(n_pages) - 1;
                GEM_BUG_ON(order > mem->mm.max_order);
                GEM_BUG_ON(order < min_order);
 

diff --git a/drivers/gpu/drm/i915/intel_memory_region.h b/drivers/gpu/drm/i915/intel_memory_region.h
index 5fb9bcf..232490d 100644 (file)
--- a/drivers/gpu/drm/i915/intel_memory_region.h
+++ b/drivers/gpu/drm/i915/intel_memory_region.h
@@ -44,9 +44,8 @@ enum intel_region_id {
 #define MEMORY_TYPE_FROM_REGION(r) (ilog2((r) >> INTEL_MEMORY_TYPE_SHIFT))
 #define MEMORY_INSTANCE_FROM_REGION(r) (ilog2((r) & 0xffff))
 
-#define I915_ALLOC_MIN_PAGE_SIZE       BIT(0)
-#define I915_ALLOC_CONTIGUOUS          BIT(1)
-#define I915_ALLOC_MAX_SEGMENT_SIZE    BIT(2)
+#define I915_ALLOC_MIN_PAGE_SIZE  BIT(0)
+#define I915_ALLOC_CONTIGUOUS     BIT(1)
 
 #define for_each_memory_region(mr, i915, id) \
        for (id = 0; id < ARRAY_SIZE((i915)->mm.regions); id++) \

diff --git a/drivers/gpu/drm/i915/selftests/intel_memory_region.c b/drivers/gpu/drm/i915/selftests/intel_memory_region.c
index 7c02a0c..a0b518c 100644 (file)
--- a/drivers/gpu/drm/i915/selftests/intel_memory_region.c
+++ b/drivers/gpu/drm/i915/selftests/intel_memory_region.c
@@ -356,21 +356,21 @@ out_put:
 
 static int igt_mock_max_segment(void *arg)
 {
+       const unsigned int max_segment = i915_sg_segment_size();
        struct intel_memory_region *mem = arg;
        struct drm_i915_private *i915 = mem->i915;
        struct drm_i915_gem_object *obj;
        struct i915_buddy_block *block;
+       struct scatterlist *sg;
        LIST_HEAD(objects);
        u64 size;
        int err = 0;
 
        /*
-        * The size of block are only limited by the largest power-of-two that
-        * will fit in the region size, but to construct an object we also
-        * require feeding it into an sg list, where the upper limit of the sg
-        * entry is at most UINT_MAX, therefore when allocating with
-        * I915_ALLOC_MAX_SEGMENT_SIZE we shouldn't see blocks larger than
-        * i915_sg_segment_size().
+        * While we may create very large contiguous blocks, we may need
+        * to break those down for consumption elsewhere. In particular,
+        * dma-mapping with scatterlist elements have an implicit limit of
+        * UINT_MAX on each element.
         */
 
        size = SZ_8G;
@@ -384,12 +384,23 @@ static int igt_mock_max_segment(void *arg)
                goto out_put;
        }
 
+       err = -EINVAL;
        list_for_each_entry(block, &obj->mm.blocks, link) {
-               if (i915_buddy_block_size(&mem->mm, block) > i915_sg_segment_size()) {
-                       pr_err("%s found block size(%llu) larger than max sg_segment_size(%u)",
-                              __func__,
-                              i915_buddy_block_size(&mem->mm, block),
-                              i915_sg_segment_size());
+               if (i915_buddy_block_size(&mem->mm, block) > max_segment) {
+                       err = 0;
+                       break;
+               }
+       }
+       if (err) {
+               pr_err("%s: Failed to create a huge contiguous block\n",
+                      __func__);
+               goto out_close;
+       }
+
+       for (sg = obj->mm.pages->sgl; sg; sg = sg_next(sg)) {
+               if (sg->length > max_segment) {
+                       pr_err("%s: Created an oversized scatterlist entry, %u > %u\n",
+                              __func__, sg->length, max_segment);
                        err = -EINVAL;
                        goto out_close;
                }