[Qemu-devel] [PATCH v2 19/19] target-mips: don't flush extra TLB on permissions upgrade

[Aurelien Jarno <aurelien@aurel32.net>]

If the guest uses a TLBWI instruction for upgrading permissions, we
don't need to flush the extra TLBs. This improve boot time performance
by about 10%.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
---
 target-mips/op_helper.c |   28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/target-mips/op_helper.c b/target-mips/op_helper.c
index cdd6880..f45d494 100644
--- a/target-mips/op_helper.c
+++ b/target-mips/op_helper.c
@@ -1819,14 +1819,32 @@ static void r4k_fill_tlb(CPUMIPSState *env, int idx)
 
 void r4k_helper_tlbwi(CPUMIPSState *env)
 {
+    r4k_tlb_t *tlb;
     int idx;
+    target_ulong VPN;
+    uint8_t ASID;
+    bool G, V0, D0, V1, D1;
 
     idx = (env->CP0_Index & ~0x80000000) % env->tlb->nb_tlb;
-
-    /* Discard cached TLB entries.  We could avoid doing this if the
-       tlbwi is just upgrading access permissions on the current entry;
-       that might be a further win.  */
-    r4k_mips_tlb_flush_extra (env, env->tlb->nb_tlb);
+    tlb = &env->tlb->mmu.r4k.tlb[idx];
+    VPN = env->CP0_EntryHi & (TARGET_PAGE_MASK << 1);
+#if defined(TARGET_MIPS64)
+    VPN &= env->SEGMask;
+#endif
+    ASID = env->CP0_EntryHi & 0xff;
+    G = env->CP0_EntryLo0 & env->CP0_EntryLo1 & 1;
+    V0 = (env->CP0_EntryLo0 & 2) != 0;
+    D0 = (env->CP0_EntryLo0 & 4) != 0;
+    V1 = (env->CP0_EntryLo1 & 2) != 0;
+    D1 = (env->CP0_EntryLo1 & 4) != 0;
+
+    /* Discard cached TLB entries, unless tlbwi is just upgrading access
+       permissions on the current entry. */
+    if (tlb->VPN != VPN || tlb->ASID != ASID || tlb->G != G ||
+        (tlb->V0 && !V0) || (tlb->D0 && !D0) ||
+        (tlb->V1 && !V1) || (tlb->D1 && !D1)) {
+        r4k_mips_tlb_flush_extra(env, env->tlb->nb_tlb);
+    }
 
     r4k_invalidate_tlb(env, idx, 0);
     r4k_fill_tlb(env, idx);
-- 
1.7.10.4