Since we can control placement in the ppGTT explicitly, we can specify
our desired starting offset exactly on a per-vma basis. This prevents us
falling down a few corner cases where we confuse the user with our choices.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
 .../gpu/drm/i915/gem/i915_gem_execbuffer.c    | 67 +++++++++----------
 1 file changed, 31 insertions(+), 36 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c 
b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 19cab5541dbc..0839397c7e50 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -36,6 +36,7 @@ struct eb_vma {
 
        /** This vma's place in the execbuf reservation list */
        struct drm_i915_gem_exec_object2 *exec;
+       u32 bias;
 
        struct list_head bind_link;
        struct list_head unbound_link;
@@ -61,15 +62,12 @@ struct eb_vma_array {
 #define __EXEC_OBJECT_HAS_PIN          BIT(31)
 #define __EXEC_OBJECT_HAS_FENCE                BIT(30)
 #define __EXEC_OBJECT_NEEDS_MAP                BIT(29)
-#define __EXEC_OBJECT_NEEDS_BIAS       BIT(28)
-#define __EXEC_OBJECT_INTERNAL_FLAGS   (~0u << 28) /* all of the above */
+#define __EXEC_OBJECT_INTERNAL_FLAGS   (~0u << 29) /* all of the above */
 
 #define __EXEC_HAS_RELOC       BIT(31)
 #define __EXEC_INTERNAL_FLAGS  (~0u << 31)
 #define UPDATE                 PIN_OFFSET_FIXED
 
-#define BATCH_OFFSET_BIAS (256*1024)
-
 #define __I915_EXEC_ILLEGAL_FLAGS \
        (__I915_EXEC_UNKNOWN_FLAGS | \
         I915_EXEC_CONSTANTS_MASK  | \
@@ -291,7 +289,7 @@ struct i915_execbuffer {
        } parser;
 
        u64 invalid_flags; /** Set of execobj.flags that are invalid */
-       u32 context_flags; /** Set of execobj.flags to insert from the ctx */
+       u32 context_bias;
 
        u32 batch_start_offset; /** Location within object of batch */
        u32 batch_len; /** Length of batch within object */
@@ -491,11 +489,12 @@ static int eb_create(struct i915_execbuffer *eb)
        return 0;
 }
 
-static bool
-eb_vma_misplaced(const struct drm_i915_gem_exec_object2 *entry,
-                const struct i915_vma *vma,
-                unsigned int flags)
+static bool eb_vma_misplaced(const struct eb_vma *ev)
 {
+       const struct drm_i915_gem_exec_object2 *entry = ev->exec;
+       const struct i915_vma *vma = ev->vma;
+       unsigned int flags = ev->flags;
+
        if (test_bit(I915_VMA_ERROR_BIT, __i915_vma_flags(vma)))
                return true;
 
@@ -509,8 +508,7 @@ eb_vma_misplaced(const struct drm_i915_gem_exec_object2 
*entry,
            vma->node.start != entry->offset)
                return true;
 
-       if (flags & __EXEC_OBJECT_NEEDS_BIAS &&
-           vma->node.start < BATCH_OFFSET_BIAS)
+       if (vma->node.start < ev->bias)
                return true;
 
        if (!(flags & EXEC_OBJECT_SUPPORTS_48B_ADDRESS) &&
@@ -529,10 +527,7 @@ static bool eb_pin_vma_fence_inplace(struct eb_vma *ev)
        return false; /* We need to add some new fence serialisation */
 }
 
-static inline bool
-eb_pin_vma_inplace(struct i915_execbuffer *eb,
-                  const struct drm_i915_gem_exec_object2 *entry,
-                  struct eb_vma *ev)
+static inline bool eb_pin_vma_inplace(struct eb_vma *ev)
 {
        struct i915_vma *vma = ev->vma;
        unsigned int pin_flags;
@@ -541,7 +536,7 @@ eb_pin_vma_inplace(struct i915_execbuffer *eb,
        if (!i915_active_is_idle(&vma->vm->binding))
                return false;
 
-       if (eb_vma_misplaced(entry, vma, ev->flags))
+       if (eb_vma_misplaced(ev))
                return false;
 
        pin_flags = PIN_USER;
@@ -559,7 +554,7 @@ eb_pin_vma_inplace(struct i915_execbuffer *eb,
                }
        }
 
-       GEM_BUG_ON(eb_vma_misplaced(entry, vma, ev->flags));
+       GEM_BUG_ON(eb_vma_misplaced(ev));
 
        ev->flags |= __EXEC_OBJECT_HAS_PIN;
        return true;
@@ -608,9 +603,6 @@ eb_validate_vma(struct i915_execbuffer *eb,
                        entry->flags |= EXEC_OBJECT_NEEDS_GTT | 
__EXEC_OBJECT_NEEDS_MAP;
        }
 
-       if (!(entry->flags & EXEC_OBJECT_PINNED))
-               entry->flags |= eb->context_flags;
-
        return 0;
 }
 
@@ -627,6 +619,7 @@ eb_add_vma(struct i915_execbuffer *eb,
        ev->vma = vma;
        ev->exec = entry;
        ev->flags = entry->flags;
+       ev->bias = eb->context_bias;
 
        if (eb->lut_size > 0) {
                ev->handle = entry->handle;
@@ -653,7 +646,8 @@ eb_add_vma(struct i915_execbuffer *eb,
        if (i == batch_idx) {
                if (entry->relocation_count &&
                    !(ev->flags & EXEC_OBJECT_PINNED))
-                       ev->flags |= __EXEC_OBJECT_NEEDS_BIAS;
+                       ev->bias = max_t(u32, ev->bias, SZ_256K);
+
                if (eb->has_fence)
                        ev->flags |= EXEC_OBJECT_NEEDS_FENCE;
 
@@ -979,8 +973,9 @@ static int eb_reserve_vma(struct eb_vm_work *work, struct 
eb_bind_vma *bind)
        const unsigned int exec_flags = bind->ev->flags;
        struct i915_vma *vma = bind->ev->vma;
        struct i915_address_space *vm = vma->vm;
-       u64 start = 0, end = vm->total;
        u64 align = entry->alignment ?: I915_GTT_MIN_ALIGNMENT;
+       u64 start = round_up(bind->ev->bias, align);
+       u64 end = vm->total;
        unsigned int bind_flags;
        int err;
 
@@ -999,7 +994,7 @@ static int eb_reserve_vma(struct eb_vm_work *work, struct 
eb_bind_vma *bind)
        GEM_BUG_ON(!vma->size);
 
        /* Reuse old address (if it doesn't conflict with new requirements) */
-       if (eb_vma_misplaced(entry, vma, exec_flags)) {
+       if (eb_vma_misplaced(bind->ev)) {
                vma->node.start = entry->offset & PIN_OFFSET_MASK;
                vma->node.size = max(entry->pad_to_size, vma->size);
                vma->node.color = 0;
@@ -1021,11 +1016,8 @@ static int eb_reserve_vma(struct eb_vm_work *work, 
struct eb_bind_vma *bind)
                align = max_t(u64, align, vma->fence_alignment);
        }
 
-       if (exec_flags & __EXEC_OBJECT_NEEDS_BIAS)
-               start = BATCH_OFFSET_BIAS;
-
        GEM_BUG_ON(!vma->node.size);
-       if (vma->node.size > end - start)
+       if (start > end || vma->node.size > end - start)
                return -E2BIG;
 
        /* Try the user's preferred location first (mandatory if soft-pinned) */
@@ -1108,7 +1100,7 @@ static int eb_reserve_vma(struct eb_vm_work *work, struct 
eb_bind_vma *bind)
        }
 
        bind->ev->flags |= __EXEC_OBJECT_HAS_PIN;
-       GEM_BUG_ON(eb_vma_misplaced(entry, vma, bind->ev->flags));
+       GEM_BUG_ON(eb_vma_misplaced(bind->ev));
 
        if (unlikely(exec_flags & EXEC_OBJECT_NEEDS_FENCE)) {
                err = __i915_vma_pin_fence_async(vma, &work->base);
@@ -1341,8 +1333,7 @@ static int wait_for_unbinds(struct i915_execbuffer *eb,
 
                GEM_BUG_ON(ev->flags & __EXEC_OBJECT_HAS_PIN);
 
-               if (drm_mm_node_allocated(&vma->node) &&
-                   eb_vma_misplaced(ev->exec, vma, ev->flags)) {
+               if (drm_mm_node_allocated(&vma->node) && eb_vma_misplaced(ev)) {
                        err = i915_vma_unbind(vma);
                        if (err)
                                return err;
@@ -1391,10 +1382,10 @@ static int eb_reserve_vm(struct i915_execbuffer *eb)
        count = 0;
        INIT_LIST_HEAD(&unbound);
        list_for_each_entry(ev, &eb->bind_list, bind_link) {
-               struct drm_i915_gem_exec_object2 *entry = ev->exec;
-               struct i915_vma *vma = ev->vma;
+               if (eb_pin_vma_inplace(ev)) {
+                       struct drm_i915_gem_exec_object2 *entry = ev->exec;
+                       struct i915_vma *vma = ev->vma;
 
-               if (eb_pin_vma_inplace(eb, entry, ev)) {
                        if (entry != &no_entry &&
                            entry->offset != vma->node.start) {
                                entry->offset = vma->node.start | UPDATE;
@@ -1478,7 +1469,7 @@ static int eb_reserve_vm(struct i915_execbuffer *eb)
                         * we cannot handle migrating the vma inside the worker.
                         */
                        if (drm_mm_node_allocated(&vma->node)) {
-                               if (eb_vma_misplaced(ev->exec, vma, ev->flags)) 
{
+                               if (eb_vma_misplaced(ev)) {
                                        err = -ENOSPC;
                                        break;
                                }
@@ -1736,9 +1727,13 @@ static int eb_select_context(struct i915_execbuffer *eb)
        if (rcu_access_pointer(ctx->vm))
                eb->invalid_flags |= EXEC_OBJECT_NEEDS_GTT;
 
-       eb->context_flags = 0;
+       /*
+        * At the user's discretion, ensure that we place no objects at
+        * offset 0, allowing them to use 0 as a 'NULL' pointer.
+        */
+       eb->context_bias = 0;
        if (test_bit(UCONTEXT_NO_ZEROMAP, &ctx->user_flags))
-               eb->context_flags |= __EXEC_OBJECT_NEEDS_BIAS;
+               eb->context_bias = I915_GTT_MIN_ALIGNMENT;
 
        return 0;
 }
-- 
2.20.1

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