target/nios2: Clean up handling of tlbmisc in do_exception

The 4 lower bits, D, PERM, BAD, DBL, are unconditionally set on any
exception with EH=0, or so says Table 42 (Processor Status After
Taking Exception).

We currently do not set PERM or BAD at all, and only set/clear
DBL for tlb miss, and do not clear DBL for any other exception.

It is a bit confusing to set D in tlb_fill and the rest during
do_interrupt, so move the setting of D to do_interrupt as well.
To do this, split EXP_TLBD into two cases, EXCP_TLB_X and EXCP_TLB_D,
which allows us to distinguish them during do_interrupt.  Choose
a value for EXCP_TLB_D such that when truncated it produces the
correct value for exception.CAUSE.

Rename EXCP_TLB[RWX] to EXCP_PERM_[RWX], to emphasize that the
exception is permissions related.  Rename EXCP_SUPER[AD] to
EXCP_SUPERA_[DX] to emphasize that they are both "supervisor
address" exceptions, data and execute.

Retain the setting of tlbmisc.WE for the fast-tlb-miss path, as it
is being relied upon, but remove it from the permission path.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220421151735.31996-37-richard.henderson@linaro.org>

2 files changed, 73 insertions, 37 deletions

diff --git a/target/nios2/cpu.h b/target/nios2/cpu.h
index 01cead5..0027416 100644
--- a/target/nios2/cpu.h
+++ b/target/nios2/cpu.h
@@ -166,13 +166,14 @@ FIELD(CR_TLBMISC, EE, 24, 1)
 #define EXCP_UNALIGN  6
 #define EXCP_UNALIGND 7
 #define EXCP_DIV      8
-#define EXCP_SUPERA   9
+#define EXCP_SUPERA_X 9
 #define EXCP_SUPERI   10
-#define EXCP_SUPERD   11
-#define EXCP_TLBD     12
-#define EXCP_TLBX     13
-#define EXCP_TLBR     14
-#define EXCP_TLBW     15
+#define EXCP_SUPERA_D 11
+#define EXCP_TLB_X    12
+#define EXCP_TLB_D    (0x1000 | EXCP_TLB_X)
+#define EXCP_PERM_X   13
+#define EXCP_PERM_R   14
+#define EXCP_PERM_W   15
 #define EXCP_MPUI     16
 #define EXCP_MPUD     17
 
diff --git a/target/nios2/helper.c b/target/nios2/helper.c
index 3d98694..4d9085f 100644
--- a/target/nios2/helper.c
+++ b/target/nios2/helper.c
@@ -29,7 +29,8 @@
 #include "semihosting/semihost.h"
 
 
-static void do_exception(Nios2CPU *cpu, uint32_t exception_addr, bool is_break)
+static void do_exception(Nios2CPU *cpu, uint32_t exception_addr,
+                         uint32_t tlbmisc_set, bool is_break)
 {
     CPUNios2State *env = &cpu->env;
     CPUState *cs = CPU(cpu);
@@ -48,6 +49,16 @@ static void do_exception(Nios2CPU *cpu, uint32_t exception_addr, bool is_break)
 
         if (cpu->mmu_present) {
             new_status |= CR_STATUS_EH;
+
+            /*
+             * There are 4 bits that are always written.
+             * Explicitly clear them, to be set via the argument.
+             */
+            env->ctrl[CR_TLBMISC] &= ~(CR_TLBMISC_D |
+                                       CR_TLBMISC_PERM |
+                                       CR_TLBMISC_BAD |
+                                       CR_TLBMISC_DBL);
+            env->ctrl[CR_TLBMISC] |= tlbmisc_set;
         }
     }
 
@@ -63,13 +74,14 @@ static void do_exception(Nios2CPU *cpu, uint32_t exception_addr, bool is_break)
 
 static void do_iic_irq(Nios2CPU *cpu)
 {
-    do_exception(cpu, cpu->exception_addr, false);
+    do_exception(cpu, cpu->exception_addr, 0, false);
 }
 
 void nios2_cpu_do_interrupt(CPUState *cs)
 {
     Nios2CPU *cpu = NIOS2_CPU(cs);
     CPUNios2State *env = &cpu->env;
+    uint32_t tlbmisc_set = 0;
 
     if (qemu_loglevel_mask(CPU_LOG_INT)) {
         const char *name = NULL;
@@ -78,20 +90,21 @@ void nios2_cpu_do_interrupt(CPUState *cs)
         case EXCP_IRQ:
             name = "interrupt";
             break;
-        case EXCP_TLBD:
+        case EXCP_TLB_X:
+        case EXCP_TLB_D:
             if (env->ctrl[CR_STATUS] & CR_STATUS_EH) {
                 name = "TLB MISS (double)";
             } else {
                 name = "TLB MISS (fast)";
             }
             break;
-        case EXCP_TLBR:
-        case EXCP_TLBW:
-        case EXCP_TLBX:
+        case EXCP_PERM_R:
+        case EXCP_PERM_W:
+        case EXCP_PERM_X:
             name = "TLB PERM";
             break;
-        case EXCP_SUPERA:
-        case EXCP_SUPERD:
+        case EXCP_SUPERA_X:
+        case EXCP_SUPERA_D:
             name = "SUPERVISOR (address)";
             break;
         case EXCP_SUPERI:
@@ -129,38 +142,57 @@ void nios2_cpu_do_interrupt(CPUState *cs)
         do_iic_irq(cpu);
         break;
 
-    case EXCP_TLBD:
-        if ((env->ctrl[CR_STATUS] & CR_STATUS_EH) == 0) {
-            env->ctrl[CR_TLBMISC] &= ~CR_TLBMISC_DBL;
-            env->ctrl[CR_TLBMISC] |= CR_TLBMISC_WE;
-            do_exception(cpu, cpu->fast_tlb_miss_addr, false);
+    case EXCP_TLB_D:
+        tlbmisc_set = CR_TLBMISC_D;
+        /* fall through */
+    case EXCP_TLB_X:
+        if (env->ctrl[CR_STATUS] & CR_STATUS_EH) {
+            tlbmisc_set |= CR_TLBMISC_DBL;
+            /*
+             * Normally, we don't write to tlbmisc unless !EH,
+             * so do it manually for the double-tlb miss exception.
+             */
+            env->ctrl[CR_TLBMISC] &= ~(CR_TLBMISC_D |
+                                       CR_TLBMISC_PERM |
+                                       CR_TLBMISC_BAD);
+            env->ctrl[CR_TLBMISC] |= tlbmisc_set;
+            do_exception(cpu, cpu->exception_addr, 0, false);
         } else {
-            env->ctrl[CR_TLBMISC] |= CR_TLBMISC_DBL;
-            do_exception(cpu, cpu->exception_addr, false);
+            tlbmisc_set |= CR_TLBMISC_WE;
+            do_exception(cpu, cpu->fast_tlb_miss_addr, tlbmisc_set, false);
         }
         break;
 
-    case EXCP_TLBR:
-    case EXCP_TLBW:
-    case EXCP_TLBX:
-        if ((env->ctrl[CR_STATUS] & CR_STATUS_EH) == 0) {
-            env->ctrl[CR_TLBMISC] |= CR_TLBMISC_WE;
+    case EXCP_PERM_R:
+    case EXCP_PERM_W:
+        tlbmisc_set = CR_TLBMISC_D;
+        /* fall through */
+    case EXCP_PERM_X:
+        tlbmisc_set |= CR_TLBMISC_PERM;
+        if (!(env->ctrl[CR_STATUS] & CR_STATUS_EH)) {
+            tlbmisc_set |= CR_TLBMISC_WE;
         }
-        do_exception(cpu, cpu->exception_addr, false);
+        do_exception(cpu, cpu->exception_addr, tlbmisc_set, false);
+        break;
+
+    case EXCP_SUPERA_D:
+    case EXCP_UNALIGN:
+        tlbmisc_set = CR_TLBMISC_D;
+        /* fall through */
+    case EXCP_SUPERA_X:
+    case EXCP_UNALIGND:
+        tlbmisc_set |= CR_TLBMISC_BAD;
+        do_exception(cpu, cpu->exception_addr, tlbmisc_set, false);
         break;
 
-    case EXCP_SUPERA:
     case EXCP_SUPERI:
-    case EXCP_SUPERD:
     case EXCP_ILLEGAL:
     case EXCP_TRAP:
-    case EXCP_UNALIGN:
-    case EXCP_UNALIGND:
-        do_exception(cpu, cpu->exception_addr, false);
+        do_exception(cpu, cpu->exception_addr, 0, false);
         break;
 
     case EXCP_BREAK:
-        do_exception(cpu, cpu->exception_addr, true);
+        do_exception(cpu, cpu->exception_addr, 0, true);
         break;
 
     case EXCP_SEMIHOST:
@@ -215,7 +247,7 @@ bool nios2_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
 {
     Nios2CPU *cpu = NIOS2_CPU(cs);
     CPUNios2State *env = &cpu->env;
-    unsigned int excp = EXCP_TLBD;
+    unsigned int excp;
     target_ulong vaddr, paddr;
     Nios2MMULookup lu;
     unsigned int hit;
@@ -242,7 +274,8 @@ bool nios2_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
             if (probe) {
                 return false;
             }
-            cs->exception_index = EXCP_SUPERA;
+            cs->exception_index = (access_type == MMU_INST_FETCH
+                                   ? EXCP_SUPERA_X : EXCP_SUPERA_D);
             env->ctrl[CR_BADADDR] = address;
             cpu_loop_exit_restore(cs, retaddr);
         }
@@ -263,8 +296,10 @@ bool nios2_cpu_tlb_fill(CPUState *cs, vaddr address, int size,
         }
 
         /* Permission violation */
-        excp = (access_type == MMU_DATA_LOAD ? EXCP_TLBR :
-                access_type == MMU_DATA_STORE ? EXCP_TLBW : EXCP_TLBX);
+        excp = (access_type == MMU_DATA_LOAD ? EXCP_PERM_R :
+                access_type == MMU_DATA_STORE ? EXCP_PERM_W : EXCP_PERM_X);
+    } else {
+        excp = (access_type == MMU_INST_FETCH ? EXCP_TLB_X: EXCP_TLB_D);
     }
 
     if (probe) {