On Wed, Sep 22, 2021 at 01:05:12PM +0200, Peter Zijlstra wrote:
quoted hunk ↗ jump to hunk
---
include/linux/context_tracking_state.h | 12 ++++++++++++
kernel/context_tracking.c | 7 ++++---
2 files changed, 16 insertions(+), 3 deletions(-)
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -45,11 +45,23 @@ static __always_inline bool context_trac
{
return __this_cpu_read(context_tracking.state) == CONTEXT_USER;
}
+
+static __always_inline bool context_tracking_state_cpu(int cpu)
+{
+ struct context_tracking *ct = per_cpu_ptr(&context_tracking);
+
+ if (!context_tracking_enabled() || !ct->active)
+ return CONTEXT_DISABLED;
+
+ return ct->state;
+}
+
#else
static inline bool context_tracking_in_user(void) { return false; }
static inline bool context_tracking_enabled(void) { return false; }
static inline bool context_tracking_enabled_cpu(int cpu) { return false; }
static inline bool context_tracking_enabled_this_cpu(void) { return false; }
+static inline bool context_tracking_state_cpu(int cpu) { return CONTEXT_DISABLED; }
#endif /* CONFIG_CONTEXT_TRACKING */
#endif
Should context_tracking_state_cpu return an enum ctx_state rather than a
bool? It appears to be doing an implicit cast.
I don't know if it possible to run livepatch with
CONFIG_CONTEXT_TRACKING disabled, but if so, then klp_check_task() as
modified by patch 7 will always consider the transition complete even if
the current task is in kernel mode. Also in the general case, the CPU
will consider the task complete if has ctx_state CONTEXT_GUEST though the
condition does not make it explicit.
I'm not sure what the correct behavior should be here as I am not very
experienced with this sybsystem but the patch looks a bit odd to me.
quoted hunk ↗ jump to hunk
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -82,7 +82,7 @@ void noinstr __context_tracking_enter(en
vtime_user_enter(current);
instrumentation_end();
}
- rcu_user_enter();
+ rcu_user_enter(); /* smp_mb */
}
/*
* Even if context tracking is disabled on this CPU, because it's outside
@@ -149,12 +149,14 @@ void noinstr __context_tracking_exit(enu
return;
if (__this_cpu_read(context_tracking.state) == state) {
+ __this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
+
if (__this_cpu_read(context_tracking.active)) {
/*
* We are going to run code that may use RCU. Inform
* RCU core about that (ie: we may need the tick again).
*/
- rcu_user_exit();
+ rcu_user_exit(); /* smp_mb */
if (state == CONTEXT_USER) {
instrumentation_begin();
vtime_user_exit(current);@@ -162,7 +164,6 @@ void noinstr __context_tracking_exit(enu
instrumentation_end();
}
}
- __this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
}
context_tracking_recursion_exit();
}