On powerpc, we need to do some lockless pagetable walks from functions
that already have disabled interrupts, specially from real mode with
MSR[EE=0].
In these contexts, disabling/enabling interrupts can be very troubling.
So, this arch-specific implementation features functions with an extra
argument that allows interrupt enable/disable to be skipped:
__begin_lockless_pgtbl_walk() and __end_lockless_pgtbl_walk().
Functions similar to the generic ones are also exported, by calling
the above functions with parameter {en,dis}able_irq = true.
Signed-off-by: Leonardo Bras <leonardo@xxxxxxxxxxxxx>
---
arch/powerpc/include/asm/book3s/64/pgtable.h | 6 ++
arch/powerpc/mm/book3s64/pgtable.c | 86 +++++++++++++++++++-
2 files changed, 91 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 201a69e6a355..78f6ffb1bb3e 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -1375,5 +1375,11 @@ static inline bool pgd_is_leaf(pgd_t pgd)
return !!(pgd_raw(pgd) & cpu_to_be64(_PAGE_PTE));
}
+#define __HAVE_ARCH_LOCKLESS_PGTBL_WALK_CONTROL
+unsigned long begin_lockless_pgtbl_walk(void);
+unsigned long __begin_lockless_pgtbl_walk(bool disable_irq);
+void end_lockless_pgtbl_walk(unsigned long irq_mask);
+void __end_lockless_pgtbl_walk(unsigned long irq_mask, bool enable_irq);
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_POWERPC_BOOK3S_64_PGTABLE_H_ */
diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c
index 2bf7e1b4fd82..535613030363 100644
--- a/arch/powerpc/mm/book3s64/pgtable.c
+++ b/arch/powerpc/mm/book3s64/pgtable.c
@@ -82,6 +82,7 @@ static void do_nothing(void *unused)
{
}
+
/*
* Serialize against find_current_mm_pte which does lock-less
* lookup in page tables with local interrupts disabled. For huge pages
@@ -98,6 +99,89 @@ void serialize_against_pte_lookup(struct mm_struct *mm)
smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1);
}
+/* begin_lockless_pgtbl_walk: Must be inserted before a function call that does
+ * lockless pagetable walks, such as __find_linux_pte().
+ * This version allows setting disable_irq=false, so irqs are not touched, which
+ * is quite useful for running when ints are already disabled (like real-mode)
+ */
+inline
+unsigned long __begin_lockless_pgtbl_walk(bool disable_irq)
+{
+ unsigned long irq_mask = 0;
+
+ /*
+ * Interrupts must be disabled during the lockless page table walk.
+ * That's because the deleting or splitting involves flushing TLBs,
+ * which in turn issues interrupts, that will block when disabled.
+ *
+ * When this function is called from realmode with MSR[EE=0],
+ * it's not needed to touch irq, since it's already disabled.
+ */
+ if (disable_irq)
+ local_irq_save(irq_mask);
+
+ /*
+ * This memory barrier pairs with any code that is either trying to
+ * delete page tables, or split huge pages. Without this barrier,
+ * the page tables could be read speculatively outside of interrupt
+ * disabling or reference counting.
+ */
+ smp_mb();
+
+ return irq_mask;
+}
+EXPORT_SYMBOL(__begin_lockless_pgtbl_walk);
+
+/* begin_lockless_pgtbl_walk: Must be inserted before a function call that does
+ * lockless pagetable walks, such as __find_linux_pte().
+ * This version is used by generic code, and always assume irqs will be disabled
+ */
+unsigned long begin_lockless_pgtbl_walk(void)
+{
+ return __begin_lockless_pgtbl_walk(true);
+}
+EXPORT_SYMBOL(begin_lockless_pgtbl_walk);
+
+/*
+ * __end_lockless_pgtbl_walk: Must be inserted after the last use of a pointer
+ * returned by a lockless pagetable walk, such as __find_linux_pte()
+ * This version allows setting enable_irq=false, so irqs are not touched, which
+ * is quite useful for running when ints are already disabled (like real-mode)
+ */
+inline void __end_lockless_pgtbl_walk(unsigned long irq_mask, bool enable_irq)
+{
+ /*
+ * This memory barrier pairs with any code that is either trying to
+ * delete page tables, or split huge pages. Without this barrier,
+ * the page tables could be read speculatively outside of interrupt
+ * disabling or reference counting.
+ */
+ smp_mb();
+
+ /*
+ * Interrupts must be disabled during the lockless page table walk.
+ * That's because the deleting or splitting involves flushing TLBs,
+ * which in turn issues interrupts, that will block when disabled.
+ *
+ * When this function is called from realmode with MSR[EE=0],
+ * it's not needed to touch irq, since it's already disabled.
+ */
+ if (enable_irq)
+ local_irq_restore(irq_mask);
+}
+EXPORT_SYMBOL(__end_lockless_pgtbl_walk);
+
+/*
+ * end_lockless_pgtbl_walk: Must be inserted after the last use of a pointer
+ * returned by a lockless pagetable walk, such as __find_linux_pte()
+ * This version is used by generic code, and always assume irqs will be enabled
+ */
+void end_lockless_pgtbl_walk(unsigned long irq_mask)
+{
+ __end_lockless_pgtbl_walk(irq_mask, true);
+}
+EXPORT_SYMBOL(end_lockless_pgtbl_walk);
+
/*
* We use this to invalidate a pmdp entry before switching from a
* hugepte to regular pmd entry.
@@ -487,7 +571,7 @@ static int __init setup_disable_tlbie(char *str)
tlbie_capable = false;
tlbie_enabled = false;
- return 1;
+ return 1;
}
__setup("disable_tlbie", setup_disable_tlbie);
--
2.24.1
