riscv: Make __flush_tlb_range() loop over pte instead of flushing the whole tlb

Currently, when the range to flush covers more than one page (a 4K page or
a hugepage), __flush_tlb_range() flushes the whole tlb. Flushing the whole
tlb comes with a greater cost than flushing a single entry so we should
flush single entries up to a certain threshold so that:
threshold * cost of flushing a single entry < cost of flushing the whole
tlb.

Co-developed-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> # On RZ/Five SMARC
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Tested-by: Samuel Holland <samuel.holland@sifive.com>
Link: https://lore.kernel.org/r/20231030133027.19542-4-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

1 files changed, 59 insertions, 56 deletions

diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index b6d712a82306..e46fefc70927 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -9,28 +9,50 @@
 
 static inline void local_flush_tlb_all_asid(unsigned long asid)
 {
-	__asm__ __volatile__ ("sfence.vma x0, %0"
-			:
-			: "r" (asid)
-			: "memory");
+	if (asid != FLUSH_TLB_NO_ASID)
+		__asm__ __volatile__ ("sfence.vma x0, %0"
+				:
+				: "r" (asid)
+				: "memory");
+	else
+		local_flush_tlb_all();
 }
 
 static inline void local_flush_tlb_page_asid(unsigned long addr,
 		unsigned long asid)
 {
-	__asm__ __volatile__ ("sfence.vma %0, %1"
-			:
-			: "r" (addr), "r" (asid)
-			: "memory");
+	if (asid != FLUSH_TLB_NO_ASID)
+		__asm__ __volatile__ ("sfence.vma %0, %1"
+				:
+				: "r" (addr), "r" (asid)
+				: "memory");
+	else
+		local_flush_tlb_page(addr);
 }
 
-static inline void local_flush_tlb_range(unsigned long start,
-		unsigned long size, unsigned long stride)
+/*
+ * Flush entire TLB if number of entries to be flushed is greater
+ * than the threshold below.
+ */
+static unsigned long tlb_flush_all_threshold __read_mostly = 64;
+
+static void local_flush_tlb_range_threshold_asid(unsigned long start,
+						 unsigned long size,
+						 unsigned long stride,
+						 unsigned long asid)
 {
-	if (size <= stride)
-		local_flush_tlb_page(start);
-	else
-		local_flush_tlb_all();
+	unsigned long nr_ptes_in_range = DIV_ROUND_UP(size, stride);
+	int i;
+
+	if (nr_ptes_in_range > tlb_flush_all_threshold) {
+		local_flush_tlb_all_asid(asid);
+		return;
+	}
+
+	for (i = 0; i < nr_ptes_in_range; ++i) {
+		local_flush_tlb_page_asid(start, asid);
+		start += stride;
+	}
 }
 
 static inline void local_flush_tlb_range_asid(unsigned long start,
@@ -38,8 +60,10 @@ static inline void local_flush_tlb_range_asid(unsigned long start,
 {
 	if (size <= stride)
 		local_flush_tlb_page_asid(start, asid);
-	else
+	else if (size == FLUSH_TLB_MAX_SIZE)
 		local_flush_tlb_all_asid(asid);
+	else
+		local_flush_tlb_range_threshold_asid(start, size, stride, asid);
 }
 
 static void __ipi_flush_tlb_all(void *info)
@@ -52,7 +76,7 @@ void flush_tlb_all(void)
 	if (riscv_use_ipi_for_rfence())
 		on_each_cpu(__ipi_flush_tlb_all, NULL, 1);
 	else
-		sbi_remote_sfence_vma(NULL, 0, -1);
+		sbi_remote_sfence_vma_asid(NULL, 0, FLUSH_TLB_MAX_SIZE, FLUSH_TLB_NO_ASID);
 }
 
 struct flush_tlb_range_data {
@@ -69,18 +93,12 @@ static void __ipi_flush_tlb_range_asid(void *info)
 	local_flush_tlb_range_asid(d->start, d->size, d->stride, d->asid);
 }
 
-static void __ipi_flush_tlb_range(void *info)
-{
-	struct flush_tlb_range_data *d = info;
-
-	local_flush_tlb_range(d->start, d->size, d->stride);
-}
-
 static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 			      unsigned long size, unsigned long stride)
 {
 	struct flush_tlb_range_data ftd;
 	struct cpumask *cmask = mm_cpumask(mm);
+	unsigned long asid = FLUSH_TLB_NO_ASID;
 	unsigned int cpuid;
 	bool broadcast;
 
@@ -90,39 +108,24 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 	cpuid = get_cpu();
 	/* check if the tlbflush needs to be sent to other CPUs */
 	broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
-	if (static_branch_unlikely(&use_asid_allocator)) {
-		unsigned long asid = atomic_long_read(&mm->context.id) & asid_mask;
-
-		if (broadcast) {
-			if (riscv_use_ipi_for_rfence()) {
-				ftd.asid = asid;
-				ftd.start = start;
-				ftd.size = size;
-				ftd.stride = stride;
-				on_each_cpu_mask(cmask,
-						 __ipi_flush_tlb_range_asid,
-						 &ftd, 1);
-			} else
-				sbi_remote_sfence_vma_asid(cmask,
-							   start, size, asid);
-		} else {
-			local_flush_tlb_range_asid(start, size, stride, asid);
-		}
+
+	if (static_branch_unlikely(&use_asid_allocator))
+		asid = atomic_long_read(&mm->context.id) & asid_mask;
+
+	if (broadcast) {
+		if (riscv_use_ipi_for_rfence()) {
+			ftd.asid = asid;
+			ftd.start = start;
+			ftd.size = size;
+			ftd.stride = stride;
+			on_each_cpu_mask(cmask,
+					 __ipi_flush_tlb_range_asid,
+					 &ftd, 1);
+		} else
+			sbi_remote_sfence_vma_asid(cmask,
+						   start, size, asid);
 	} else {
-		if (broadcast) {
-			if (riscv_use_ipi_for_rfence()) {
-				ftd.asid = 0;
-				ftd.start = start;
-				ftd.size = size;
-				ftd.stride = stride;
-				on_each_cpu_mask(cmask,
-						 __ipi_flush_tlb_range,
-						 &ftd, 1);
-			} else
-				sbi_remote_sfence_vma(cmask, start, size);
-		} else {
-			local_flush_tlb_range(start, size, stride);
-		}
+		local_flush_tlb_range_asid(start, size, stride, asid);
 	}
 
 	put_cpu();
@@ -130,7 +133,7 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 
 void flush_tlb_mm(struct mm_struct *mm)
 {
-	__flush_tlb_range(mm, 0, -1, PAGE_SIZE);
+	__flush_tlb_range(mm, 0, FLUSH_TLB_MAX_SIZE, PAGE_SIZE);
 }
 
 void flush_tlb_mm_range(struct mm_struct *mm,