From: Anup Patel <apatel@ventanamicro.com>
Date: Wed, 18 Jun 2025 11:35:25 +0000 (+0530)
Subject: RISC-V: KVM: Don't flush TLB when PTE is unchanged
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=eaa98ba20be088eeb252061f216c299442ba5a69;p=thirdparty%2Fkernel%2Flinux.git

RISC-V: KVM: Don't flush TLB when PTE is unchanged

The gstage_set_pte() and gstage_op_pte() should flush TLB only when
a leaf PTE changes so that unnecessary TLB flushes can be avoided.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Tested-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Nutty Liu <liujingqi@lanxincomputing.com>
Link: https://lore.kernel.org/r/20250618113532.471448-6-apatel@ventanamicro.com
Signed-off-by: Anup Patel <anup@brainfault.org>
---

diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
index 1087ea74567b4..29f1bd853a669 100644
--- a/arch/riscv/kvm/mmu.c
+++ b/arch/riscv/kvm/mmu.c
@@ -167,9 +167,11 @@ static int gstage_set_pte(struct kvm *kvm, u32 level,
 		ptep = &next_ptep[gstage_pte_index(addr, current_level)];
 	}
 
-	set_pte(ptep, *new_pte);
-	if (gstage_pte_leaf(ptep))
-		gstage_remote_tlb_flush(kvm, current_level, addr);
+	if (pte_val(*ptep) != pte_val(*new_pte)) {
+		set_pte(ptep, *new_pte);
+		if (gstage_pte_leaf(ptep))
+			gstage_remote_tlb_flush(kvm, current_level, addr);
+	}
 
 	return 0;
 }
@@ -229,7 +231,7 @@ static void gstage_op_pte(struct kvm *kvm, gpa_t addr,
 			  pte_t *ptep, u32 ptep_level, enum gstage_op op)
 {
 	int i, ret;
-	pte_t *next_ptep;
+	pte_t old_pte, *next_ptep;
 	u32 next_ptep_level;
 	unsigned long next_page_size, page_size;
 
@@ -258,11 +260,13 @@ static void gstage_op_pte(struct kvm *kvm, gpa_t addr,
 		if (op == GSTAGE_OP_CLEAR)
 			put_page(virt_to_page(next_ptep));
 	} else {
+		old_pte = *ptep;
 		if (op == GSTAGE_OP_CLEAR)
 			set_pte(ptep, __pte(0));
 		else if (op == GSTAGE_OP_WP)
 			set_pte(ptep, __pte(pte_val(ptep_get(ptep)) & ~_PAGE_WRITE));
-		gstage_remote_tlb_flush(kvm, ptep_level, addr);
+		if (pte_val(*ptep) != pte_val(old_pte))
+			gstage_remote_tlb_flush(kvm, ptep_level, addr);
 	}
 }