gregkh@xxxxxxxxxxxxxxxxxxx writes:
> The patch below does not apply to the 4.12-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
Here it is.
cheers
From: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 24 Jul 2017 14:28:00 +1000
Subject: [PATCH] powerpc/mm: Ensure cpumask update is ordered
commit 1a92a80ad386a1a6e3b36d576d52a1a456394b70 upstream.
There is no guarantee that the various isync's involved with
the context switch will order the update of the CPU mask with
the first TLB entry for the new context being loaded by the HW.
Be safe here and add a memory barrier to order any subsequent
load/store which may bring entries into the TLB.
The corresponding barrier on the other side already exists as
pte updates use pte_xchg() which uses __cmpxchg_u64 which has
a sync after the atomic operation.
Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Nicholas Piggin <npiggin@xxxxxxxxx>
[mpe: Backport to 4.12, minor context change]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
---
arch/powerpc/include/asm/mmu_context.h | 20 +++++++++++++++++++-
arch/powerpc/include/asm/pgtable-be-types.h | 1 +
arch/powerpc/include/asm/pgtable-types.h | 1 +
3 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index da7e9432fa8f..db80b301c080 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -80,9 +80,27 @@ static inline void switch_mm_irqs_off(struct mm_struct *prev,
struct task_struct *tsk)
{
/* Mark this context has been used on the new CPU */
- if (!cpumask_test_cpu(smp_processor_id(), mm_cpumask(next)))
+ if (!cpumask_test_cpu(smp_processor_id(), mm_cpumask(next))) {
cpumask_set_cpu(smp_processor_id(), mm_cpumask(next));
+ /*
+ * This full barrier orders the store to the cpumask above vs
+ * a subsequent operation which allows this CPU to begin loading
+ * translations for next.
+ *
+ * When using the radix MMU that operation is the load of the
+ * MMU context id, which is then moved to SPRN_PID.
+ *
+ * For the hash MMU it is either the first load from slb_cache
+ * in switch_slb(), and/or the store of paca->mm_ctx_id in
+ * copy_mm_to_paca().
+ *
+ * On the read side the barrier is in pte_xchg(), which orders
+ * the store to the PTE vs the load of mm_cpumask.
+ */
+ smp_mb();
+ }
+
/* 32-bit keeps track of the current PGDIR in the thread struct */
#ifdef CONFIG_PPC32
tsk->thread.pgdir = next->pgd;
diff --git a/arch/powerpc/include/asm/pgtable-be-types.h b/arch/powerpc/include/asm/pgtable-be-types.h
index 9c0f5db5cf46..67e7e3d990f4 100644
--- a/arch/powerpc/include/asm/pgtable-be-types.h
+++ b/arch/powerpc/include/asm/pgtable-be-types.h
@@ -87,6 +87,7 @@ static inline bool pte_xchg(pte_t *ptep, pte_t old, pte_t new)
unsigned long *p = (unsigned long *)ptep;
__be64 prev;
+ /* See comment in switch_mm_irqs_off() */
prev = (__force __be64)__cmpxchg_u64(p, (__force unsigned long)pte_raw(old),
(__force unsigned long)pte_raw(new));
diff --git a/arch/powerpc/include/asm/pgtable-types.h b/arch/powerpc/include/asm/pgtable-types.h
index 8bd3b13fe2fb..369a164b545c 100644
--- a/arch/powerpc/include/asm/pgtable-types.h
+++ b/arch/powerpc/include/asm/pgtable-types.h
@@ -62,6 +62,7 @@ static inline bool pte_xchg(pte_t *ptep, pte_t old, pte_t new)
{
unsigned long *p = (unsigned long *)ptep;
+ /* See comment in switch_mm_irqs_off() */
return pte_val(old) == __cmpxchg_u64(p, pte_val(old), pte_val(new));
}
#endif
--
2.7.4