[RFC PATCH v2 2/2] 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 PTRS_PER_PTE. 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 |  12 ++++
 arch/riscv/kernel/setup.c         |   1 +
 arch/riscv/mm/tlbflush.c          | 116 ++++++++++++++++++++++++++++--
 3 files changed, 123 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index 801019381dea..b535467c99f0 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -22,6 +22,18 @@ static inline void local_flush_tlb_page(unsigned long addr)
 {
 	ALT_FLUSH_TLB_PAGE(__asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory"));
 }
+
+void riscv_tlbflush_init(void);
+void __riscv_sfence_w_inval(void);
+void __riscv_sfence_inval_ir(void);
+void __riscv_sinval_vma(unsigned long addr);
+void __riscv_sinval_vma_asid(unsigned long addr, unsigned long asid);
+
+/* Check if we can use sinval for tlb flush */
+DECLARE_STATIC_KEY_FALSE(riscv_flush_tlb_svinval);
+#define riscv_use_flush_tlb_svinval() \
+	static_branch_unlikely(&riscv_flush_tlb_svinval)
+
 #else /* CONFIG_MMU */
 #define local_flush_tlb_all()			do { } while (0)
 #define local_flush_tlb_page(addr)		do { } while (0)
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 834eb652a7b9..13de04259de9 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -295,6 +295,7 @@ void __init setup_arch(char **cmdline_p)
 #endif
 
 	riscv_fill_hwcap();
+	riscv_tlbflush_init();
 }
 
 static int __init topology_init(void)
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 27a7db8eb2c4..800953f9121e 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -1,11 +1,14 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#define pr_fmt(fmt) "riscv: " fmt
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/sched.h>
 #include <asm/sbi.h>
 #include <asm/mmu_context.h>
 
+static unsigned long tlb_flush_all_threshold __read_mostly = PTRS_PER_PTE;
+
 static inline void local_flush_tlb_all_asid(unsigned long asid)
 {
 	__asm__ __volatile__ ("sfence.vma x0, %0"
@@ -23,22 +26,110 @@ static inline void local_flush_tlb_page_asid(unsigned long addr,
 			: "memory");
 }
 
+static inline void riscv_sfence_inval_ir(void)
+{
+	/*
+	 * SFENCE.INVAL.IR
+	 * 0001100 00001 00000 000 00000 1110011
+	 */
+	asm volatile (".word 0x18100073" ::: "memory");
+}
+
+static inline void riscv_sfence_w_inval(void)
+{
+	/*
+	 * SFENCE.W.INVAL
+	 * 0001100 00000 00000 000 00000 1110011
+	 */
+	asm volatile (".word 0x18000073" ::: "memory");
+}
+
+static inline void riscv_sinval_vma_asid(unsigned long vma, unsigned long asid)
+{
+	/*
+	 * rs1 = a0 (VMA)
+	 * rs2 = a1 (asid)
+	 * SINVAL.VMA a0, a1
+	 * 0001011 01011 01010 000 00000 1110011
+	 */
+	asm volatile ("srli a0, %0, 2\n"
+			"add a1, %1, zero\n"
+			".word 0x16B50073\n"
+			:: "r" (vma), "r" (asid)
+			: "a0", "a1", "memory");
+}
+
+static inline void riscv_sinval_vma(unsigned long vma)
+{
+	/*
+	 * rs1 = a0 (VMA)
+	 * rs2 = 0
+	 * SINVAL.VMA a0
+	 * 0001011 00000 01010 000 00000 1110011
+	 */
+	asm volatile ("srli a0, %0, 2\n"
+			".word 0x16050073\n"
+			:: "r" (vma) : "a0", "memory");
+}
+
 static inline void local_flush_tlb_range(unsigned long start,
 		unsigned long size, unsigned long stride)
 {
-	if (size <= stride)
-		local_flush_tlb_page(start);
-	else
+	if ((size / stride) <= tlb_flush_all_threshold) {
+		if (riscv_use_flush_tlb_svinval()) {
+			riscv_sfence_w_inval();
+			while (size) {
+				riscv_sinval_vma(start);
+				start += stride;
+				if (size > stride)
+					size -= stride;
+				else
+					size = 0;
+			}
+			riscv_sfence_inval_ir();
+		} else {
+			while (size) {
+				local_flush_tlb_page(start);
+				start += stride;
+				if (size > stride)
+					size -= stride;
+				else
+					size = 0;
+			}
+		}
+	} else {
 		local_flush_tlb_all();
+	}
 }
 
 static inline void local_flush_tlb_range_asid(unsigned long start,
 		unsigned long size, unsigned long stride, unsigned long asid)
 {
-	if (size <= stride)
-		local_flush_tlb_page_asid(start, asid);
-	else
+	if ((size / stride) <= tlb_flush_all_threshold) {
+		if (riscv_use_flush_tlb_svinval()) {
+			riscv_sfence_w_inval();
+			while (size) {
+				riscv_sinval_vma_asid(start, asid);
+				start += stride;
+				if (size > stride)
+					size -= stride;
+				else
+					size = 0;
+			}
+			riscv_sfence_inval_ir();
+		} else {
+			while (size) {
+				local_flush_tlb_page_asid(start, asid);
+				start += stride;
+				if (size > stride)
+					size -= stride;
+				else
+					size = 0;
+			}
+		}
+	} else {
 		local_flush_tlb_all_asid(asid);
+	}
 }
 
 static void __ipi_flush_tlb_all(void *info)
@@ -149,3 +240,16 @@ void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
 	__flush_tlb_range(vma->vm_mm, start, end - start, PMD_SIZE);
 }
 #endif
+
+DEFINE_STATIC_KEY_FALSE(riscv_flush_tlb_svinval);
+EXPORT_SYMBOL_GPL(riscv_flush_tlb_svinval);
+
+void riscv_tlbflush_init(void)
+{
+	if (riscv_isa_extension_available(NULL, SVINVAL)) {
+		pr_info("Svinval extension supported\n");
+		static_branch_enable(&riscv_flush_tlb_svinval);
+	} else {
+		static_branch_disable(&riscv_flush_tlb_svinval);
+	}
+}
-- 
2.17.1