drm/i915: Report context GTT size

Since the beginning we have conflated the size of the global GTT with
that of the per-process context sizes. In recent times (gen8+), those
are no longer the same where the global GTT is limited to 2/4GiB but the
per-process GTT may be anything up to 256TiB. Userspace knows nothing of
this discrepancy and outside of one or two hacks, uses the getaperture
ioctl to determine the maximum size it can use. Let's leave that as
reporting the global GTT and use the context reporting method to
describe the per-process value (which naturally fallsback to reporting
the aliasing or global on older platforms, so userspace can always use
this method where available).

Testcase: igt/gem_userptr_blits/minor-normal-sync
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90065
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_context.c

@@ -925,6 +925,14 @@ int i915_gem_context_getparam_ioctl(struct drm_device *dev, void *data,
 	case I915_CONTEXT_PARAM_NO_ZEROMAP:
 		args->value = ctx->flags & CONTEXT_NO_ZEROMAP;
 		break;
+	case I915_CONTEXT_PARAM_GTT_SIZE:
+		if (ctx->ppgtt)
+			args->value = ctx->ppgtt->base.total;
+		else if (to_i915(dev)->mm.aliasing_ppgtt)
+			args->value = to_i915(dev)->mm.aliasing_ppgtt->base.total;
+		else
+			args->value = to_i915(dev)->gtt.base.total;
+		break;
 	default:
 		ret = -EINVAL;
 		break;

include/uapi/drm/i915_drm.h

@@ -1125,8 +1125,9 @@ struct drm_i915_gem_context_param {
 	__u32 ctx_id;
 	__u32 size;
 	__u64 param;
-#define I915_CONTEXT_PARAM_BAN_PERIOD 0x1
-#define I915_CONTEXT_PARAM_NO_ZEROMAP 0x2
+#define I915_CONTEXT_PARAM_BAN_PERIOD	0x1
+#define I915_CONTEXT_PARAM_NO_ZEROMAP	0x2
+#define I915_CONTEXT_PARAM_GTT_SIZE	0x3
 	__u64 value;
 };