ppc/hash32: Rework R and C bit updates

With MT-TCG, we are now running translation in a racy way, thus
we need to mimic hardware when it comes to updating the R and
C bits, by doing byte stores.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20190411080004.8690-5-clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

target/ppc/mmu-hash32.c

@@ -345,6 +345,24 @@ static hwaddr ppc_hash32_pteg_search(PowerPCCPU *cpu, hwaddr pteg_off,
     return -1;
 }
 
+static void ppc_hash32_set_r(PowerPCCPU *cpu, hwaddr pte_offset, uint32_t pte1)
+{
+    target_ulong base = ppc_hash32_hpt_base(cpu);
+    hwaddr offset = pte_offset + 6;
+
+    /* The HW performs a non-atomic byte update */
+    stb_phys(CPU(cpu)->as, base + offset, ((pte1 >> 8) & 0xff) | 0x01);
+}
+
+static void ppc_hash32_set_c(PowerPCCPU *cpu, hwaddr pte_offset, uint64_t pte1)
+{
+    target_ulong base = ppc_hash32_hpt_base(cpu);
+    hwaddr offset = pte_offset + 7;
+
+    /* The HW performs a non-atomic byte update */
+    stb_phys(CPU(cpu)->as, base + offset, (pte1 & 0xff) | 0x80);
+}
+
 static hwaddr ppc_hash32_htab_lookup(PowerPCCPU *cpu,
                                      target_ulong sr, target_ulong eaddr,
                                      ppc_hash_pte32_t *pte)
@@ -403,7 +421,6 @@ int ppc_hash32_handle_mmu_fault(PowerPCCPU *cpu, vaddr eaddr, int rwx,
     hwaddr pte_offset;
     ppc_hash_pte32_t pte;
     int prot;
-    uint32_t new_pte1;
     const int need_prot[] = {PAGE_READ, PAGE_WRITE, PAGE_EXEC};
     hwaddr raddr;
 
@@ -519,20 +536,20 @@ int ppc_hash32_handle_mmu_fault(PowerPCCPU *cpu, vaddr eaddr, int rwx,
 
     /* 8. Update PTE referenced and changed bits if necessary */
 
-    new_pte1 = pte.pte1 | HPTE32_R_R; /* set referenced bit */
-    if (rwx == 1) {
-        new_pte1 |= HPTE32_R_C; /* set changed (dirty) bit */
-    } else {
-        /*
-         * Treat the page as read-only for now, so that a later write
-         * will pass through this function again to set the C bit
-         */
-        prot &= ~PAGE_WRITE;
-    }
-
-    if (new_pte1 != pte.pte1) {
-        ppc_hash32_store_hpte1(cpu, pte_offset, new_pte1);
+    if (!(pte.pte1 & HPTE32_R_R)) {
+        ppc_hash32_set_r(cpu, pte_offset, pte.pte1);
     }
+    if (!(pte.pte1 & HPTE32_R_C)) {
+        if (rwx == 1) {
+            ppc_hash32_set_c(cpu, pte_offset, pte.pte1);
+        } else {
+            /*
+             * Treat the page as read-only for now, so that a later write
+             * will pass through this function again to set the C bit
+             */
+            prot &= ~PAGE_WRITE;
+        }
+     }
 
     /* 9. Determine the real address from the PTE */