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
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);
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;
mm_ctx_user_psize(&mm->context),
mm_ctx_user_psize(&mm->context),
pte_val(*ptep));
+
+ local_irq_restore(flags);
}
/*