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* [PATCH v3 3/3] x86/mm: If INVPCID is available, use it to flush global mappings
  2016-01-29 19:42 [PATCH v3 0/3] x86/mm: INVPCID support Andy Lutomirski
@ 2016-01-29 19:42 ` Andy Lutomirski
  0 siblings, 0 replies; 1+ messages in thread
From: Andy Lutomirski @ 2016-01-29 19:42 UTC (permalink / raw)
  To: x86, linux-kernel
  Cc: Borislav Petkov, Brian Gerst, Dave Hansen, Linus Torvalds,
	Oleg Nesterov, linux-mm, Andrey Ryabinin, Andy Lutomirski

On my Skylake laptop, INVPCID function 2 (flush absolutely
everything) takes about 376ns, whereas saving flags, twiddling
CR4.PGE to flush global mappings, and restoring flags takes about
539ns.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/tlbflush.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 8b576832777e..985f1162c505 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -152,6 +152,15 @@ static inline void __native_flush_tlb_global(void)
 {
 	unsigned long flags;
 
+	if (static_cpu_has_safe(X86_FEATURE_INVPCID)) {
+		/*
+		 * Using INVPCID is considerably faster than a pair of writes
+		 * to CR4 sandwiched inside an IRQ flag save/restore.
+		 */
+		invpcid_flush_all();
+		return;
+	}
+
 	/*
 	 * Read-modify-write to CR4 - protect it from preemption and
 	 * from interrupts. (Use the raw variant because this code can
-- 
2.5.0

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2016-01-29 19:42 [PATCH v3 0/3] x86/mm: INVPCID support Andy Lutomirski
2016-01-29 19:42 ` [PATCH v3 3/3] x86/mm: If INVPCID is available, use it to flush global mappings Andy Lutomirski

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