[PATCH v2 3/3] x86/mm: If INVPCID is available, use it to flush global mappings

[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 <l...@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 20fc38d8478a..4eba5164430d 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -145,6 +145,15 @@ 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_everything();
+               return;
+       }
+
        /*
         * Read-modify-write to CR4 - protect it from preemption and
         * from interrupts. (Use the raw variant because this code can
-- 
2.5.0