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-rw-r--r--arch/x86/include/asm/tlbflush.h21
1 files changed, 15 insertions, 6 deletions
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index d362161d3291..c4aed0de565e 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -82,12 +82,21 @@ static inline u64 inc_mm_tlb_gen(struct mm_struct *mm)
#define __flush_tlb_single(addr) __native_flush_tlb_single(addr)
#endif
-/*
- * If tlb_use_lazy_mode is true, then we try to avoid switching CR3 to point
- * to init_mm when we switch to a kernel thread (e.g. the idle thread). If
- * it's false, then we immediately switch CR3 when entering a kernel thread.
- */
-DECLARE_STATIC_KEY_TRUE(tlb_use_lazy_mode);
+static inline bool tlb_defer_switch_to_init_mm(void)
+{
+ /*
+ * If we have PCID, then switching to init_mm is reasonably
+ * fast. If we don't have PCID, then switching to init_mm is
+ * quite slow, so we try to defer it in the hopes that we can
+ * avoid it entirely. The latter approach runs the risk of
+ * receiving otherwise unnecessary IPIs.
+ *
+ * This choice is just a heuristic. The tlb code can handle this
+ * function returning true or false regardless of whether we have
+ * PCID.
+ */
+ return !static_cpu_has(X86_FEATURE_PCID);
+}
/*
* 6 because 6 should be plenty and struct tlb_state will fit in