[RESEND PATCH v10 02/12] arm64: tlbflush: add APIs manipulating tlb batch's arch data

[Byungchul Park <byungchul@sk.com>]

A new mechanism, LUF(Lazy Unmap Flush), defers tlb flush until folios
that have been unmapped and freed, eventually get allocated again.  It's
safe for folios that had been mapped read only and were unmapped, since
the contents of the folios don't change while staying in pcp or buddy
so we can still read the data through the stale tlb entries.

This is a preparation for the mechanism that requires to manipulate tlb
batch's arch data.  Even though arm64 does nothing for tlb things, arch
with CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH should provide the APIs.

Signed-off-by: Byungchul Park <byungchul@sk.com>
---
 arch/arm64/include/asm/tlbflush.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
index a75de2665d84..b8c7fbc1c68e 100644
--- a/arch/arm64/include/asm/tlbflush.h
+++ b/arch/arm64/include/asm/tlbflush.h
@@ -347,6 +347,24 @@ static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
 	dsb(ish);
 }
 
+static inline void arch_tlbbatch_clear(struct arch_tlbflush_unmap_batch *batch)
+{
+	/* nothing to do */
+}
+
+static inline void arch_tlbbatch_fold(struct arch_tlbflush_unmap_batch *bdst,
+			       struct arch_tlbflush_unmap_batch *bsrc)
+{
+	/* nothing to do */
+}
+
+static inline bool arch_tlbbatch_done(struct arch_tlbflush_unmap_batch *bdst,
+			       struct arch_tlbflush_unmap_batch *bsrc)
+{
+	/* Kernel can consider tlb batch always has been done. */
+	return true;
+}
+
 /*
  * This is meant to avoid soft lock-ups on large TLB flushing ranges and not
  * necessarily a performance improvement.
-- 
2.17.1