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-rw-r--r--arch/powerpc/kernel/exceptions-64s.S14
-rw-r--r--arch/powerpc/mm/book3s64/hash_utils.c25
-rw-r--r--arch/powerpc/perf/core-book3s.c6
3 files changed, 42 insertions, 3 deletions
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 0fc8bad878b2..446e54c3f71e 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -3072,10 +3072,18 @@ do_hash_page:
ori r0,r0,DSISR_BAD_FAULT_64S@l
and. r0,r5,r0 /* weird error? */
bne- handle_page_fault /* if not, try to insert a HPTE */
+
+ /*
+ * If we are in an "NMI" (e.g., an interrupt when soft-disabled), then
+ * don't call hash_page, just fail the fault. This is required to
+ * prevent re-entrancy problems in the hash code, namely perf
+ * interrupts hitting while something holds H_PAGE_BUSY, and taking a
+ * hash fault. See the comment in hash_preload().
+ */
ld r11, PACA_THREAD_INFO(r13)
- lwz r0,TI_PREEMPT(r11) /* If we're in an "NMI" */
- andis. r0,r0,NMI_MASK@h /* (i.e. an irq when soft-disabled) */
- bne 77f /* then don't call hash_page now */
+ lwz r0,TI_PREEMPT(r11)
+ andis. r0,r0,NMI_MASK@h
+ bne 77f
/*
* r3 contains the trap number
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 468169e33c86..9b9f92ad0e7a 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -1559,6 +1559,7 @@ static void hash_preload(struct mm_struct *mm, pte_t *ptep, unsigned long ea,
pgd_t *pgdir;
int rc, ssize, update_flags = 0;
unsigned long access = _PAGE_PRESENT | _PAGE_READ | (is_exec ? _PAGE_EXEC : 0);
+ unsigned long flags;
BUG_ON(get_region_id(ea) != USER_REGION_ID);
@@ -1592,6 +1593,28 @@ static void hash_preload(struct mm_struct *mm, pte_t *ptep, unsigned long ea,
return;
#endif /* CONFIG_PPC_64K_PAGES */
+ /*
+ * __hash_page_* must run with interrupts off, as it sets the
+ * H_PAGE_BUSY bit. It's possible for perf interrupts to hit at any
+ * time and may take a hash fault reading the user stack, see
+ * read_user_stack_slow() in the powerpc/perf code.
+ *
+ * If that takes a hash fault on the same page as we lock here, it
+ * will bail out when seeing H_PAGE_BUSY set, and retry the access
+ * leading to an infinite loop.
+ *
+ * Disabling interrupts here does not prevent perf interrupts, but it
+ * will prevent them taking hash faults (see the NMI test in
+ * do_hash_page), then read_user_stack's copy_from_user_nofault will
+ * fail and perf will fall back to read_user_stack_slow(), which
+ * walks the Linux page tables.
+ *
+ * Interrupts must also be off for the duration of the
+ * mm_is_thread_local test and update, to prevent preempt running the
+ * mm on another CPU (XXX: this may be racy vs kthread_use_mm).
+ */
+ local_irq_save(flags);
+
/* Is that local to this CPU ? */
if (mm_is_thread_local(mm))
update_flags |= HPTE_LOCAL_UPDATE;
@@ -1614,6 +1637,8 @@ static void hash_preload(struct mm_struct *mm, pte_t *ptep, unsigned long ea,
mm_ctx_user_psize(&mm->context),
mm_ctx_user_psize(&mm->context),
pte_val(*ptep));
+
+ local_irq_restore(flags);
}
/*
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index cd6a742ac6ef..01d70280d287 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2179,6 +2179,12 @@ static void __perf_event_interrupt(struct pt_regs *regs)
perf_read_regs(regs);
+ /*
+ * If perf interrupts hit in a local_irq_disable (soft-masked) region,
+ * we consider them as NMIs. This is required to prevent hash faults on
+ * user addresses when reading callchains. See the NMI test in
+ * do_hash_page.
+ */
nmi = perf_intr_is_nmi(regs);
if (nmi)
nmi_enter();