[PATCH v4 03/13] 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 called even/odd
pages. Supposing even/odd page is normal/none state, when odd page
is added, TLB entry is changed as normal/normal state and even page
keeps unchanged.

In this situation, it is not necessary to flush QEMU TLB since even
page keep unchanged and odd page is newly changed. 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>
Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
---
 target/loongarch/tcg/tlb_helper.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/target/loongarch/tcg/tlb_helper.c 
b/target/loongarch/tcg/tlb_helper.c
index 25dbbd0d77..88dba9eb3e 100644
--- a/target/loongarch/tcg/tlb_helper.c
+++ b/target/loongarch/tcg/tlb_helper.c
@@ -302,16 +302,35 @@ 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);
+    fill_tlb_entry(env, &new);
+    /* Check whether ASID/VPPN is the same */
+    if (old->tlb_misc == new.tlb_misc) {
+        /* Check whether both even/odd pages 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 = new;
 }
 
 void helper_tlbfill(CPULoongArchState *env)
-- 
2.39.3