[patch 06/12] perf_event_open: check for block interference CPUs

[Marcelo Tosatti <mtosatti@redhat.com>]

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-isolation/kernel/events/core.c
===================================================================
--- linux-isolation.orig/kernel/events/core.c
+++ linux-isolation/kernel/events/core.c
@@ -55,6 +55,7 @@
 #include <linux/pgtable.h>
 #include <linux/buildid.h>
 #include <linux/task_work.h>
+#include <linux/sched/isolation.h>
 
 #include "internal.h"
 
@@ -12435,6 +12436,7 @@ SYSCALL_DEFINE5(perf_event_open,
 	int err;
 	int f_flags = O_RDWR;
 	int cgroup_fd = -1;
+	int idx;
 
 	/* for future expandability... */
 	if (flags & ~PERF_FLAG_ALL)
@@ -12712,6 +12714,26 @@ SYSCALL_DEFINE5(perf_event_open,
 		goto err_context;
 	}
 
+	idx = block_interf_srcu_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.
@@ -12775,6 +12797,8 @@ SYSCALL_DEFINE5(perf_event_open,
 		put_task_struct(task);
 	}
 
+	block_interf_srcu_read_unlock(idx);
+
 	mutex_lock(&current->perf_event_mutex);
 	list_add_tail(&event->owner_entry, &current->perf_event_list);
 	mutex_unlock(&current->perf_event_mutex);
@@ -12789,6 +12813,8 @@ SYSCALL_DEFINE5(perf_event_open,
 	fd_install(event_fd, event_file);
 	return event_fd;
 
+err_block_interf:
+	block_interf_srcu_read_unlock(idx);
 err_context:
 	put_pmu_ctx(event->pmu_ctx);
 	event->pmu_ctx = NULL; /* _free_event() */