[PATCH v4 18/19] target/loongarch: Reduce TLB flush with helper_tlbwr

[Bibo Mao]

With function helper_tlbwr(), specified LoongArch TLB entry will be
updated. There are two PTE pages in one TLB entry, it is not
necessary to flush QEMU TLB when one PTE page keeps unchanged and
ther other PTE page is newly added.

Here check whether PTE page is the same or not, TLB flush can be
skipped if both are the same or newly added.

Signed-off-by: Bibo Mao <maob...@loongson.cn>
---
 target/loongarch/tcg/tlb_helper.c | 33 ++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/target/loongarch/tcg/tlb_helper.c 
b/target/loongarch/tcg/tlb_helper.c
index 888a008944..0013810c50 100644
--- a/target/loongarch/tcg/tlb_helper.c
+++ b/target/loongarch/tcg/tlb_helper.c
@@ -313,16 +313,39 @@ void helper_tlbrd(CPULoongArchState *env)
 void helper_tlbwr(CPULoongArchState *env)
 {
     int index = FIELD_EX64(env->CSR_TLBIDX, CSR_TLBIDX, INDEX);
+    LoongArchTLB *old, new;
+    bool skip_inv = false;
+    uint8_t tlb_v0, tlb_v1;
 
-    invalidate_tlb(env, index);
-
+    old = env->tlb + index;
     if (FIELD_EX64(env->CSR_TLBIDX, CSR_TLBIDX, NE)) {
-        env->tlb[index].tlb_misc = FIELD_DP64(env->tlb[index].tlb_misc,
-                                              TLB_MISC, E, 0);
+        invalidate_tlb(env, index);
+        old->tlb_misc = FIELD_DP64(old->tlb_misc, TLB_MISC, E, 0);
         return;
     }
 
-    fill_tlb_entry(env, env->tlb + index);
+    new.tlb_misc = 0;
+    new.tlb_entry0 = 0;
+    new.tlb_entry1 = 0;
+    fill_tlb_entry(env, &new);
+    /* Check whether ASID/VPPN is the same */
+    if (old->tlb_misc == new.tlb_misc) {
+        /* Check whether pte is the same or invalid */
+        tlb_v0 = FIELD_EX64(old->tlb_entry0, TLBENTRY, V);
+        tlb_v1 = FIELD_EX64(old->tlb_entry1, TLBENTRY, V);
+        if ((!tlb_v0 || new.tlb_entry0 == old->tlb_entry0) &&
+            (!tlb_v1 || new.tlb_entry1 == old->tlb_entry1)) {
+            skip_inv = true;
+        }
+    }
+
+    /* flush tlb before updating the entry */
+    if (!skip_inv) {
+        invalidate_tlb(env, index);
+    }
+    old->tlb_misc = new.tlb_misc;
+    old->tlb_entry0 = new.tlb_entry0;
+    old->tlb_entry1 = new.tlb_entry1;
 }
 
 void helper_tlbfill(CPULoongArchState *env)
-- 
2.39.3