accel/tcg: Avoid caching overwritten tlb entries

When installing a TLB entry, remove any cached version of the
same page in the VTLB.  If the existing TLB entry matches, do
not copy into the VTLB, but overwrite it.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/cputlb.c

@@ -235,17 +235,30 @@ void tlb_flush_by_mmuidx_all_cpus_synced(CPUState *src_cpu,
     async_safe_run_on_cpu(src_cpu, fn, RUN_ON_CPU_HOST_INT(idxmap));
 }
 
+static inline bool tlb_hit_page_anyprot(CPUTLBEntry *tlb_entry,
+                                        target_ulong page)
+{
+    return tlb_hit_page(tlb_entry->addr_read, page) ||
+           tlb_hit_page(tlb_entry->addr_write, page) ||
+           tlb_hit_page(tlb_entry->addr_code, page);
+}
 
-
-static inline void tlb_flush_entry(CPUTLBEntry *tlb_entry, target_ulong addr)
+static inline void tlb_flush_entry(CPUTLBEntry *tlb_entry, target_ulong page)
 {
-    if (tlb_hit_page(tlb_entry->addr_read, addr) ||
-        tlb_hit_page(tlb_entry->addr_write, addr) ||
-        tlb_hit_page(tlb_entry->addr_code, addr)) {
+    if (tlb_hit_page_anyprot(tlb_entry, page)) {
         memset(tlb_entry, -1, sizeof(*tlb_entry));
     }
 }
 
+static inline void tlb_flush_vtlb_page(CPUArchState *env, int mmu_idx,
+                                       target_ulong page)
+{
+    int k;
+    for (k = 0; k < CPU_VTLB_SIZE; k++) {
+        tlb_flush_entry(&env->tlb_v_table[mmu_idx][k], page);
+    }
+}
+
 static void tlb_flush_page_async_work(CPUState *cpu, run_on_cpu_data data)
 {
     CPUArchState *env = cpu->env_ptr;
@@ -271,14 +284,7 @@ static void tlb_flush_page_async_work(CPUState *cpu, run_on_cpu_data data)
     i = (addr >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
     for (mmu_idx = 0; mmu_idx < NB_MMU_MODES; mmu_idx++) {
         tlb_flush_entry(&env->tlb_table[mmu_idx][i], addr);
-    }
-
-    /* check whether there are entries that need to be flushed in the vtlb */
-    for (mmu_idx = 0; mmu_idx < NB_MMU_MODES; mmu_idx++) {
-        int k;
-        for (k = 0; k < CPU_VTLB_SIZE; k++) {
-            tlb_flush_entry(&env->tlb_v_table[mmu_idx][k], addr);
-        }
+        tlb_flush_vtlb_page(env, mmu_idx, addr);
     }
 
     tb_flush_jmp_cache(cpu, addr);
@@ -310,7 +316,6 @@ static void tlb_flush_page_by_mmuidx_async_work(CPUState *cpu,
     unsigned long mmu_idx_bitmap = addr_and_mmuidx & ALL_MMUIDX_BITS;
     int page = (addr >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
     int mmu_idx;
-    int i;
 
     assert_cpu_is_self(cpu);
 
@@ -320,11 +325,7 @@ static void tlb_flush_page_by_mmuidx_async_work(CPUState *cpu,
     for (mmu_idx = 0; mmu_idx < NB_MMU_MODES; mmu_idx++) {
         if (test_bit(mmu_idx, &mmu_idx_bitmap)) {
             tlb_flush_entry(&env->tlb_table[mmu_idx][page], addr);
-
-            /* check whether there are vltb entries that need to be flushed */
-            for (i = 0; i < CPU_VTLB_SIZE; i++) {
-                tlb_flush_entry(&env->tlb_v_table[mmu_idx][i], addr);
-            }
+            tlb_flush_vtlb_page(env, mmu_idx, addr);
         }
     }
 
@@ -609,10 +610,9 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong vaddr,
     target_ulong address;
     target_ulong code_address;
     uintptr_t addend;
-    CPUTLBEntry *te, *tv, tn;
+    CPUTLBEntry *te, tn;
     hwaddr iotlb, xlat, sz, paddr_page;
     target_ulong vaddr_page;
-    unsigned vidx = env->vtlb_index++ % CPU_VTLB_SIZE;
     int asidx = cpu_asidx_from_attrs(cpu, attrs);
 
     assert_cpu_is_self(cpu);
@@ -654,19 +654,28 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong vaddr,
         addend = (uintptr_t)memory_region_get_ram_ptr(section->mr) + xlat;
     }
 
+    /* Make sure there's no cached translation for the new page.  */
+    tlb_flush_vtlb_page(env, mmu_idx, vaddr_page);
+
     code_address = address;
     iotlb = memory_region_section_get_iotlb(cpu, section, vaddr_page,
                                             paddr_page, xlat, prot, &address);
 
     index = (vaddr_page >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
     te = &env->tlb_table[mmu_idx][index];
-    /* do not discard the translation in te, evict it into a victim tlb */
-    tv = &env->tlb_v_table[mmu_idx][vidx];
 
-    /* addr_write can race with tlb_reset_dirty_range */
-    copy_tlb_helper(tv, te, true);
+    /*
+     * Only evict the old entry to the victim tlb if it's for a
+     * different page; otherwise just overwrite the stale data.
+     */
+    if (!tlb_hit_page_anyprot(te, vaddr_page)) {
+        unsigned vidx = env->vtlb_index++ % CPU_VTLB_SIZE;
+        CPUTLBEntry *tv = &env->tlb_v_table[mmu_idx][vidx];
 
-    env->iotlb_v[mmu_idx][vidx] = env->iotlb[mmu_idx][index];
+        /* Evict the old entry into the victim tlb.  */
+        copy_tlb_helper(tv, te, true);
+        env->iotlb_v[mmu_idx][vidx] = env->iotlb[mmu_idx][index];
+    }
 
     /* refill the tlb */
     /*