[Qemu-devel] [PATCH 1/7] target/mips: compare virtual addresses in LL/SC sequence

[Aleksandar Markovic]

From: Leon Alrae <address@hidden>

Do only virtual addresses comaprisons in LL/SC sequence.

Until this patch, physical addresses had been compared in LL/SC
sequence. Unfortunately, that meant that, on each SC, the address
translation had to be done, which is a quite complex operation.
Getting rid of that allows throwing away SC helpers and having
common SC implementations in user and system mode, avoiding two
separate implementations selected by #ifdef CONFIG_USER_ONLY.

Given that LL/SC emulation was already very simplified (as only the
address and value were compared), using virtual addresses instead of
physical does not seem to be a violation. Correct guest software
should not rely on LL/SC if they accesses the same physical address
via different virtual addresses or if page mapping gets changed
between LL/SC due to manipulating TLB entries. MIPS Instruction Set
Manual clearly says that an RMW sequence must use the same address
in the LL and SC (virtual address, physical address, cacheability
and coherency attributes must be identical). Otherwise, the result of
the SC is not predictable. This patch takes advantage of this fact
and removes the virtual->physical address translation from SC helper.

lladdr served as Coprocessor 0 LLAddr register which captures physical
address of the most recent LL instruction, and also lladdr was used
for comparison with following SC physical address. This patch changes
the meaning of lladdr - now it will only keep the virtual address of
the most recent LL. Additionally we introduce CP0_LLAddr which is the
actual Coperocessor 0 LLAddr register that guest can access.

Signed-off-by: Leon Alrae <address@hidden>
Signed-off-by: Miodrag Dinic <address@hidden>
Signed-off-by: Aleksandar Markovic <address@hidden>
---
 target/mips/cpu.h       |  3 ++-
 target/mips/machine.c   |  7 ++++---
 target/mips/op_helper.c | 29 +++++++++++++++++------------
 target/mips/translate.c |  4 ++--
 4 files changed, 25 insertions(+), 18 deletions(-)

diff --git a/target/mips/cpu.h b/target/mips/cpu.h
index 7f8ba5f..57ca861 100644
--- a/target/mips/cpu.h
+++ b/target/mips/cpu.h
@@ -480,10 +480,11 @@ struct CPUMIPSState {
 #define CP0C5_NFExists   0
     int32_t CP0_Config6;
     int32_t CP0_Config7;
+    uint64_t CP0_LLAddr;
     uint64_t CP0_MAAR[MIPS_MAAR_MAX];
     int32_t CP0_MAARI;
     /* XXX: Maybe make LLAddr per-TC? */
-    uint64_t lladdr;
+    target_ulong lladdr; /* LL virtual address compared against SC */
     target_ulong llval;
     target_ulong llnewval;
     target_ulong llreg;
diff --git a/target/mips/machine.c b/target/mips/machine.c
index 20100d5..155170c 100644
--- a/target/mips/machine.c
+++ b/target/mips/machine.c
@@ -212,8 +212,8 @@ const VMStateDescription vmstate_tlb = {
 
 const VMStateDescription vmstate_mips_cpu = {
     .name = "cpu",
-    .version_id = 10,
-    .minimum_version_id = 10,
+    .version_id = 11,
+    .minimum_version_id = 11,
     .post_load = cpu_post_load,
     .fields = (VMStateField[]) {
         /* Active TC */
@@ -283,9 +283,10 @@ const VMStateDescription vmstate_mips_cpu = {
         VMSTATE_INT32(env.CP0_Config3, MIPSCPU),
         VMSTATE_INT32(env.CP0_Config6, MIPSCPU),
         VMSTATE_INT32(env.CP0_Config7, MIPSCPU),
+        VMSTATE_UINT64(env.CP0_LLAddr, MIPSCPU),
         VMSTATE_UINT64_ARRAY(env.CP0_MAAR, MIPSCPU, MIPS_MAAR_MAX),
         VMSTATE_INT32(env.CP0_MAARI, MIPSCPU),
-        VMSTATE_UINT64(env.lladdr, MIPSCPU),
+        VMSTATE_UINTTL(env.lladdr, MIPSCPU),
         VMSTATE_UINTTL_ARRAY(env.CP0_WatchLo, MIPSCPU, 8),
         VMSTATE_INT32_ARRAY(env.CP0_WatchHi, MIPSCPU, 8),
         VMSTATE_UINTTL(env.CP0_XContext, MIPSCPU),
diff --git a/target/mips/op_helper.c b/target/mips/op_helper.c
index e537a8b..283669c 100644
--- a/target/mips/op_helper.c
+++ b/target/mips/op_helper.c
@@ -255,15 +255,15 @@ static inline hwaddr do_translate_address(CPUMIPSState 
*env,
                                                       target_ulong address,
                                                       int rw, uintptr_t 
retaddr)
 {
-    hwaddr lladdr;
+    hwaddr paddr;
     CPUState *cs = CPU(mips_env_get_cpu(env));
 
-    lladdr = cpu_mips_translate_address(env, address, rw);
+    paddr = cpu_mips_translate_address(env, address, rw);
 
-    if (lladdr == -1LL) {
+    if (paddr == -1LL) {
         cpu_loop_exit_restore(cs, retaddr);
     } else {
-        return lladdr;
+        return paddr;
     }
 }
 
@@ -274,7 +274,8 @@ target_ulong helper_##name(CPUMIPSState *env, target_ulong 
arg, int mem_idx)  \
         env->CP0_BadVAddr = arg;                                              \
         do_raise_exception(env, EXCP_AdEL, GETPC());                          \
     }                                                                         \
-    env->lladdr = do_translate_address(env, arg, 0, GETPC());                 \
+    env->CP0_LLAddr = do_translate_address(env, arg, 0, GETPC());             \
+    env->lladdr = arg;                                                        \
     env->llval = do_##insn(env, arg, mem_idx, GETPC());                       \
     return env->llval;                                                        \
 }
@@ -294,7 +295,7 @@ target_ulong helper_##name(CPUMIPSState *env, target_ulong 
arg1,              \
         env->CP0_BadVAddr = arg2;                                             \
         do_raise_exception(env, EXCP_AdES, GETPC());                          \
     }                                                                         \
-    if (do_translate_address(env, arg2, 1, GETPC()) == env->lladdr) {         \
+    if (arg2 == env->lladdr) {                                                \
         tmp = do_##ld_insn(env, arg2, mem_idx, GETPC());                      \
         if (tmp == env->llval) {                                              \
             do_##st_insn(env, arg2, arg1, mem_idx, GETPC());                  \
@@ -873,7 +874,7 @@ target_ulong helper_mftc0_status(CPUMIPSState *env)
 
 target_ulong helper_mfc0_lladdr(CPUMIPSState *env)
 {
-    return (int32_t)(env->lladdr >> env->CP0_LLAddr_shift);
+    return (int32_t)(env->CP0_LLAddr >> env->CP0_LLAddr_shift);
 }
 
 target_ulong helper_mfc0_maar(CPUMIPSState *env)
@@ -949,7 +950,7 @@ target_ulong helper_dmfc0_tcschefback(CPUMIPSState *env)
 
 target_ulong helper_dmfc0_lladdr(CPUMIPSState *env)
 {
-    return env->lladdr >> env->CP0_LLAddr_shift;
+    return env->CP0_LLAddr >> env->CP0_LLAddr_shift;
 }
 
 target_ulong helper_dmfc0_maar(CPUMIPSState *env)
@@ -1177,7 +1178,8 @@ void helper_mtc0_tcrestart(CPUMIPSState *env, 
target_ulong arg1)
 {
     env->active_tc.PC = arg1;
     env->active_tc.CP0_TCStatus &= ~(1 << CP0TCSt_TDS);
-    env->lladdr = 0ULL;
+    env->CP0_LLAddr = 0;
+    env->lladdr = 0;
     /* MIPS16 not implemented. */
 }
 
@@ -1189,12 +1191,14 @@ void helper_mttc0_tcrestart(CPUMIPSState *env, 
target_ulong arg1)
     if (other_tc == other->current_tc) {
         other->active_tc.PC = arg1;
         other->active_tc.CP0_TCStatus &= ~(1 << CP0TCSt_TDS);
-        other->lladdr = 0ULL;
+        other->CP0_LLAddr = 0;
+        other->lladdr = 0;
         /* MIPS16 not implemented. */
     } else {
         other->tcs[other_tc].PC = arg1;
         other->tcs[other_tc].CP0_TCStatus &= ~(1 << CP0TCSt_TDS);
-        other->lladdr = 0ULL;
+        other->CP0_LLAddr = 0;
+        other->lladdr = 0;
         /* MIPS16 not implemented. */
     }
 }
@@ -1620,7 +1624,7 @@ void helper_mtc0_lladdr(CPUMIPSState *env, target_ulong 
arg1)
 {
     target_long mask = env->CP0_LLAddr_rw_bitmask;
     arg1 = arg1 << env->CP0_LLAddr_shift;
-    env->lladdr = (env->lladdr & ~mask) | (arg1 & mask);
+    env->CP0_LLAddr = (env->CP0_LLAddr & ~mask) | (arg1 & mask);
 }
 
 #define MTC0_MAAR_MASK(env) \
@@ -2318,6 +2322,7 @@ static inline void exception_return(CPUMIPSState *env)
 void helper_eret(CPUMIPSState *env)
 {
     exception_return(env);
+    env->CP0_LLAddr = 1;
     env->lladdr = 1;
 }
 
diff --git a/target/mips/translate.c b/target/mips/translate.c
index d05ee67..c9104a7 100644
--- a/target/mips/translate.c
+++ b/target/mips/translate.c
@@ -4913,7 +4913,7 @@ static void gen_mfhc0(DisasContext *ctx, TCGv arg, int 
reg, int sel)
     case 17:
         switch (sel) {
         case 0:
-            gen_mfhc0_load64(arg, offsetof(CPUMIPSState, lladdr),
+            gen_mfhc0_load64(arg, offsetof(CPUMIPSState, CP0_LLAddr),
                              ctx->CP0_LLAddr_shift);
             rn = "LLAddr";
             break;
@@ -20440,7 +20440,7 @@ void mips_cpu_dump_state(CPUState *cs, FILE *f, 
fprintf_function cpu_fprintf,
                 env->CP0_Status, env->CP0_Cause, env->CP0_EPC);
     cpu_fprintf(f, "    Config0 0x%08x Config1 0x%08x LLAddr 0x%016"
                 PRIx64 "\n",
-                env->CP0_Config0, env->CP0_Config1, env->lladdr);
+                env->CP0_Config0, env->CP0_Config1, env->CP0_LLAddr);
     cpu_fprintf(f, "    Config2 0x%08x Config3 0x%08x\n",
                 env->CP0_Config2, env->CP0_Config3);
     cpu_fprintf(f, "    Config4 0x%08x Config5 0x%08x\n",
-- 
2.7.4