[PATCH 4.1 09/65] x86/mm, sched/core: Turn off IRQs in switch_mm()

[Pavel Tatashin]

From: Andy Lutomirski <luto@xxxxxxxxxx>

commit 078194f8e9fe3cf54c8fd8bded48a1db5bd8eb8a upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
(cherry picked from commit 4ead44fd2525ed97e5362a806d312a0e3b0ea445)
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>

Conflicts:
	arch/x86/include/asm/mmu_context.h
---
 arch/x86/include/asm/mmu_context.h |  4 ++++
 arch/x86/mm/tlb.c                  | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 375fafccb32c..2bf4bae1c65e 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -95,6 +95,10 @@ static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
 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 {						\
 	paravirt_activate_mm((prev), (next));	\
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 40c640980720..4ce6569ad963 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -63,6 +63,16 @@ 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();
 
-- 
2.16.2