When creating perf events, return an error rather
than interfering with CPUs tagged as block interference.

Note: this patch is incomplete, installation of perf context 
on block interference CPUs via task context is not performed.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: linux-2.6/kernel/events/core.c
===================================================================
--- linux-2.6.orig/kernel/events/core.c
+++ linux-2.6/kernel/events/core.c
@@ -54,6 +54,7 @@
 #include <linux/highmem.h>
 #include <linux/pgtable.h>
 #include <linux/buildid.h>
+#include <linux/sched/isolation.h>
 
 #include "internal.h"
 
@@ -12391,6 +12392,26 @@ not_move_group:
 
 	WARN_ON_ONCE(ctx->parent_ctx);
 
+	block_interf_read_lock();
+	if (!task) {
+		if (move_group) {
+			for_each_sibling_event(sibling, group_leader) {
+				if (block_interf_cpu(sibling->cpu)) {
+					err = -EPERM;
+					goto err_block_interf;
+				}
+			}
+			if (block_interf_cpu(group_leader->cpu)) {
+				err = -EPERM;
+				goto err_block_interf;
+			}
+		}
+		if (block_interf_cpu(event->cpu)) {
+			err = -EPERM;
+			goto err_block_interf;
+		}
+	}
+
 	/*
 	 * This is the point on no return; we cannot fail hereafter. This is
 	 * where we start modifying current state.
@@ -12464,6 +12485,8 @@ not_move_group:
 		put_task_struct(task);
 	}
 
+	block_interf_read_unlock();
+
 	mutex_lock(&current->perf_event_mutex);
 	list_add_tail(&event->owner_entry, &current->perf_event_list);
 	mutex_unlock(&current->perf_event_mutex);
@@ -12478,6 +12501,8 @@ not_move_group:
 	fd_install(event_fd, event_file);
 	return event_fd;
 
+err_block_interf:
+	block_interf_read_unlock();
 err_locked:
 	if (move_group)
 		perf_event_ctx_unlock(group_leader, gctx);