[MODERATED] [PATCH v6 16/43] MDSv6

[Andi Kleen <andi@firstfloor.org>]

From: Andi Kleen <ak@linux.intel.com>
Subject:  mds: Force clear cpu on kernel preemption

When the kernel is preempted we need to force a cpu clear,
because the preemption might happen before the code
has a chance to set TIF_CPU_CLEAR later.

We cannot rely on kernel code setting the flag before
touching sensitive data: the flag setting could
be implicit, like in memzero_explicit, which is always
called later.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 kernel/sched/core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d8d76a65cfdd..38e57235f4b7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11,6 +11,8 @@
 
 #include <linux/kcov.h>
 
+#include <linux/clearcpu.h>
+
 #include <asm/switch_to.h>
 #include <asm/tlb.h>
 
@@ -3632,6 +3634,13 @@ asmlinkage __visible void __sched notrace preempt_schedule(void)
 	if (likely(!preemptible()))
 		return;
 
+	/*
+	 * For kernel preemption we need to force a cpu clear
+	 * because it could happen before the code has a chance
+	 * to set TIF_CLEAR_CPU.
+	 */
+	lazy_clear_cpu();
+
 	preempt_schedule_common();
 }
 NOKPROBE_SYMBOL(preempt_schedule);
-- 
2.17.2