[tip:sched/core] x86/mm, sched/core: Turn off IRQs in switch_mm()

[tip-bot for Andy Lutomirski]

Commit-ID:  078194f8e9fe3cf54c8fd8bded48a1db5bd8eb8a
Gitweb:     http://git.kernel.org/tip/078194f8e9fe3cf54c8fd8bded48a1db5bd8eb8a
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Tue, 26 Apr 2016 09:39:09 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 28 Apr 2016 11:44:20 +0200

x86/mm, sched/core: Turn off IRQs in switch_mm()

Potential races between switch_mm() and TLB-flush or LDT-flush IPIs
could be very messy.  AFAICT the code is currently okay, whether by
accident or by careful design, but enabling PCID will make it
considerably more complicated and will no longer be obviously safe.

Fix it with a big hammer: run switch_mm() with IRQs off.

To avoid a performance hit in the scheduler, we take advantage of
our knowledge that the scheduler already has IRQs disabled when it
calls switch_mm().

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/f19baf759693c9dcae64bbff76189db77cb13398.1461688545.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/include/asm/mmu_context.h |  3 +++
 arch/x86/mm/tlb.c                  | 10 ++++++++++
 2 files changed, 13 insertions(+)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index bb911dd..39634819 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -118,6 +118,9 @@ static inline void destroy_context(struct mm_struct *mm)
 extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 		      struct task_struct *tsk);
 
+extern void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
+			       struct task_struct *tsk);
+#define switch_mm_irqs_off switch_mm_irqs_off
 
 #define activate_mm(prev, next)			\
 do {						\
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index ce7a0c9..5643fd0 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -64,6 +64,16 @@ EXPORT_SYMBOL_GPL(leave_mm);
 void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	       struct task_struct *tsk)
 {
+	unsigned long flags;
+
+	local_irq_save(flags);
+	switch_mm_irqs_off(prev, next, tsk);
+	local_irq_restore(flags);
+}
+
+void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
+			struct task_struct *tsk)
+{
 	unsigned cpu = smp_processor_id();
 
 	if (likely(prev != next)) {