linux-kernel - [PATCH v6 1/1] riscv: mm: Add support for Svinval extension

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Date: Sun,  9 Jun 2024 16:51:03 +0530
From: Mayuresh Chitale <mchitale@...tanamicro.com>
To: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: Mayuresh Chitale <mchitale@...tanamicro.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Samuel Holland <samuel.holland@...ive.com>,
	Andrew Jones <ajones@...tanamicro.com>
Subject: [PATCH v6 1/1] riscv: mm: Add support for Svinval extension

The Svinval extension splits SFENCE.VMA instruction into finer-grained
invalidation and ordering operations and is mandatory for RVA23S64 profile.
When Svinval is enabled the local_flush_tlb_range_threshold_asid function
should 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_range_threshold_asid function
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@...tanamicro.com>
---
 arch/riscv/mm/tlbflush.c | 58 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 9b6e86ce3867..49d7978ac8d3 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -6,6 +6,54 @@
 #include <linux/hugetlb.h>
 #include <asm/sbi.h>
 #include <asm/mmu_context.h>
+#include <asm/cpufeature.h>
+
+#define has_svinval()	riscv_has_extension_unlikely(RISCV_ISA_EXT_SVINVAL)
+
+static inline void local_sfence_inval_ir(void)
+{
+	/*
+	 * SFENCE.INVAL.IR
+	 * 0001100 00001 00000 000 00000 1110011
+	 */
+	__asm__ __volatile__ (".word 0x18100073" ::: "memory");
+}
+
+static inline void local_sfence_w_inval(void)
+{
+	/*
+	 * SFENCE.W.INVAL
+	 * 0001100 00000 00000 000 00000 1110011
+	 */
+	__asm__ __volatile__ (".word 0x18000073" ::: "memory");
+}
+
+static inline void local_sinval_vma_asid(unsigned long vma, unsigned long asid)
+{
+	if (asid != FLUSH_TLB_NO_ASID) {
+		/*
+		 * rs1 = a0 (VMA)
+		 * rs2 = a1 (asid)
+		 * SINVAL.VMA a0, a1
+		 * 0001011 01011 01010 000 00000 1110011
+		 */
+		__asm__ __volatile__ ("add a0, %0, zero\n"
+					"add a1, %1, zero\n"
+					".word 0x16B50073\n"
+					:: "r" (vma), "r" (asid)
+					: "a0", "a1", "memory");
+	} else {
+		/*
+		 * rs1 = a0 (VMA)
+		 * rs2 = 0
+		 * SINVAL.VMA a0
+		 * 0001011 00000 01010 000 00000 1110011
+		 */
+		__asm__ __volatile__ ("add a0, %0, zero\n"
+					".word 0x16050073\n"
+					:: "r" (vma) : "a0", "memory");
+	}
+}
 
 /*
  * Flush entire TLB if number of entries to be flushed is greater
@@ -26,6 +74,16 @@ static void local_flush_tlb_range_threshold_asid(unsigned long start,
 		return;
 	}
 
+	if (has_svinval()) {
+		local_sfence_w_inval();
+		for (i = 0; i < nr_ptes_in_range; ++i) {
+			local_sinval_vma_asid(start, asid);
+			start += stride;
+		}
+		local_sfence_inval_ir();
+		return;
+	}
+
 	for (i = 0; i < nr_ptes_in_range; ++i) {
 		local_flush_tlb_page_asid(start, asid);
 		start += stride;
-- 
2.34.1