[PATCH v5 1/1] riscv: mm: use svinval instructions instead of sfence.vma

[Mayuresh Chitale]

When svinval is supported the local_flush_tlb_page*
functions would prefer to use the following sequence
to optimize the tlb flushes instead of a simple sfence.vma:

sfence.w.inval
svinval.vma
  .
  .
svinval.vma
sfence.inval.ir

The maximum number of consecutive svinval.vma instructions
that can be executed in local_flush_tlb_page* functions is
limited to 64. This is required to avoid soft lockups and the
approach is similar to that used in arm64.

Signed-off-by: Mayuresh Chitale <mchitale at ventanamicro.com>
---
 arch/riscv/include/asm/tlbflush.h |  1 +
 arch/riscv/mm/tlbflush.c          | 66 +++++++++++++++++++++++++++----
 2 files changed, 59 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index a09196f8de68..56490c04b0bd 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -30,6 +30,7 @@ static inline void local_flush_tlb_page(unsigned long addr)
 #endif /* CONFIG_MMU */
 
 #if defined(CONFIG_SMP) && defined(CONFIG_MMU)
+extern unsigned long tlb_flush_all_threshold;
 void flush_tlb_all(void);
 void flush_tlb_mm(struct mm_struct *mm);
 void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr);
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 77be59aadc73..f63cdf8644f3 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -5,6 +5,17 @@
 #include <linux/sched.h>
 #include <asm/sbi.h>
 #include <asm/mmu_context.h>
+#include <asm/hwcap.h>
+#include <asm/insn-def.h>
+
+#define has_svinval()	riscv_has_extension_unlikely(RISCV_ISA_EXT_SVINVAL)
+
+/*
+ * Flush entire TLB if number of entries to be flushed is greater
+ * than the threshold below. Platforms may override the threshold
+ * value based on marchid, mvendorid, and mimpid.
+ */
+unsigned long tlb_flush_all_threshold __read_mostly = 64;
 
 static inline void local_flush_tlb_all_asid(unsigned long asid)
 {
@@ -24,21 +35,60 @@ static inline void local_flush_tlb_page_asid(unsigned long addr,
 }
 
 static inline void local_flush_tlb_range(unsigned long start,
-		unsigned long size, unsigned long stride)
+					 unsigned long size,
+					 unsigned long stride)
 {
-	if (size <= stride)
-		local_flush_tlb_page(start);
-	else
+	unsigned long end = start + size;
+	unsigned long num_entries = DIV_ROUND_UP(size, stride);
+
+	if (!num_entries || num_entries > tlb_flush_all_threshold) {
 		local_flush_tlb_all();
+		return;
+	}
+
+	if (has_svinval())
+		asm volatile(SFENCE_W_INVAL() ::: "memory");
+
+	while (start < end) {
+		if (has_svinval())
+			asm volatile(SINVAL_VMA(%0, zero)
+				     : : "r" (start) : "memory");
+		else
+			local_flush_tlb_page(start);
+		start += stride;
+	}
+
+	if (has_svinval())
+		asm volatile(SFENCE_INVAL_IR() ::: "memory");
 }
 
 static inline void local_flush_tlb_range_asid(unsigned long start,
-		unsigned long size, unsigned long stride, unsigned long asid)
+					      unsigned long size,
+					      unsigned long stride,
+					      unsigned long asid)
 {
-	if (size <= stride)
-		local_flush_tlb_page_asid(start, asid);
-	else
+	unsigned long end = start + size;
+	unsigned long num_entries = DIV_ROUND_UP(size, stride);
+
+	if (!num_entries || num_entries > tlb_flush_all_threshold) {
 		local_flush_tlb_all_asid(asid);
+		return;
+	}
+
+	if (has_svinval())
+		asm volatile(SFENCE_W_INVAL() ::: "memory");
+
+	while (start < end) {
+		if (has_svinval())
+			asm volatile(SINVAL_VMA(%0, %1) : : "r" (start),
+				     "r" (asid) : "memory");
+		else
+			local_flush_tlb_page_asid(start, asid);
+		start += stride;
+	}
+
+	if (has_svinval())
+		asm volatile(SFENCE_INVAL_IR() ::: "memory");
 }
 
 static void __ipi_flush_tlb_all(void *info)
-- 
2.34.1