Re: [PATCH] target/riscv: Ensure opcode is saved for every instruction

[Richard Henderson]

On 7/26/22 20:25, Anup Patel wrote:
We should call decode_save_opc() for every decoded instruction
because generating transformed instruction upon guest page faults
expects opcode to be available. Without this, hypervisor sees
transformed instruction as zero in htinst CSR for guest MMIO
emulation which makes MMIO emulation in hypervisor slow and
also breaks nested virtualization.

Then just add decode_save_opc to load/store insns, not everything including plain 
arithmetic...


r~



Fixes: a9814e3e08d2 ("target/riscv: Minimize the calls to decode_save_opc")
Signed-off-by: Anup Patel <apa...@ventanamicro.com>
---
  target/riscv/insn_trans/trans_privileged.c.inc |  4 ----
  target/riscv/insn_trans/trans_rvh.c.inc        |  2 --
  target/riscv/insn_trans/trans_rvi.c.inc        |  2 --
  target/riscv/translate.c                       | 10 ++++------
  4 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/target/riscv/insn_trans/trans_privileged.c.inc 
b/target/riscv/insn_trans/trans_privileged.c.inc
index 46f96ad74d..53613682e8 100644
--- a/target/riscv/insn_trans/trans_privileged.c.inc
+++ b/target/riscv/insn_trans/trans_privileged.c.inc
@@ -75,7 +75,6 @@ static bool trans_sret(DisasContext *ctx, arg_sret *a)
  {
  #ifndef CONFIG_USER_ONLY
      if (has_ext(ctx, RVS)) {
-        decode_save_opc(ctx);
          gen_helper_sret(cpu_pc, cpu_env);
          tcg_gen_exit_tb(NULL, 0); /* no chaining */
          ctx->base.is_jmp = DISAS_NORETURN;
@@ -91,7 +90,6 @@ static bool trans_sret(DisasContext *ctx, arg_sret *a)
  static bool trans_mret(DisasContext *ctx, arg_mret *a)
  {
  #ifndef CONFIG_USER_ONLY
-    decode_save_opc(ctx);
      gen_helper_mret(cpu_pc, cpu_env);
      tcg_gen_exit_tb(NULL, 0); /* no chaining */
      ctx->base.is_jmp = DISAS_NORETURN;
@@ -104,7 +102,6 @@ static bool trans_mret(DisasContext *ctx, arg_mret *a)
  static bool trans_wfi(DisasContext *ctx, arg_wfi *a)
  {
  #ifndef CONFIG_USER_ONLY
-    decode_save_opc(ctx);
      gen_set_pc_imm(ctx, ctx->pc_succ_insn);
      gen_helper_wfi(cpu_env);
      return true;
@@ -116,7 +113,6 @@ static bool trans_wfi(DisasContext *ctx, arg_wfi *a)
  static bool trans_sfence_vma(DisasContext *ctx, arg_sfence_vma *a)
  {
  #ifndef CONFIG_USER_ONLY
-    decode_save_opc(ctx);
      gen_helper_tlb_flush(cpu_env);
      return true;
  #endif
diff --git a/target/riscv/insn_trans/trans_rvh.c.inc 
b/target/riscv/insn_trans/trans_rvh.c.inc
index 4f8aecddc7..cebcb3f8f6 100644
--- a/target/riscv/insn_trans/trans_rvh.c.inc
+++ b/target/riscv/insn_trans/trans_rvh.c.inc
@@ -169,7 +169,6 @@ static bool trans_hfence_gvma(DisasContext *ctx, 
arg_sfence_vma *a)
  {
      REQUIRE_EXT(ctx, RVH);
  #ifndef CONFIG_USER_ONLY
-    decode_save_opc(ctx);
      gen_helper_hyp_gvma_tlb_flush(cpu_env);
      return true;
  #endif
@@ -180,7 +179,6 @@ static bool trans_hfence_vvma(DisasContext *ctx, 
arg_sfence_vma *a)
  {
      REQUIRE_EXT(ctx, RVH);
  #ifndef CONFIG_USER_ONLY
-    decode_save_opc(ctx);
      gen_helper_hyp_tlb_flush(cpu_env);
      return true;
  #endif
diff --git a/target/riscv/insn_trans/trans_rvi.c.inc 
b/target/riscv/insn_trans/trans_rvi.c.inc
index c49dbec0eb..1f318ffbef 100644
--- a/target/riscv/insn_trans/trans_rvi.c.inc
+++ b/target/riscv/insn_trans/trans_rvi.c.inc
@@ -834,8 +834,6 @@ static bool trans_fence_i(DisasContext *ctx, arg_fence_i *a)
  
  static bool do_csr_post(DisasContext *ctx)
  {
-    /* The helper may raise ILLEGAL_INSN -- record binv for unwind. */
-    decode_save_opc(ctx);
      /* We may have changed important cpu state -- exit to main loop. */
      gen_set_pc_imm(ctx, ctx->pc_succ_insn);
      tcg_gen_exit_tb(NULL, 0);
diff --git a/target/riscv/translate.c b/target/riscv/translate.c
index a79d0cd95b..5425d19846 100644
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -207,10 +207,10 @@ static void gen_check_nanbox_s(TCGv_i64 out, TCGv_i64 in)
      tcg_gen_movcond_i64(TCG_COND_GEU, out, in, t_max, in, t_nan);
  }
  
-static void decode_save_opc(DisasContext *ctx)
+static void decode_save_opc(DisasContext *ctx, target_ulong opc)
  {
      assert(ctx->insn_start != NULL);
-    tcg_set_insn_start_param(ctx->insn_start, 1, ctx->opcode);
+    tcg_set_insn_start_param(ctx->insn_start, 1, opc);
      ctx->insn_start = NULL;
  }
  
@@ -240,8 +240,6 @@ static void generate_exception(DisasContext *ctx, int excp)
  
  static void gen_exception_illegal(DisasContext *ctx)
  {
-    tcg_gen_st_i32(tcg_constant_i32(ctx->opcode), cpu_env,
-                   offsetof(CPURISCVState, bins));
      generate_exception(ctx, RISCV_EXCP_ILLEGAL_INST);
  }
  
@@ -643,8 +641,6 @@ static void gen_set_rm(DisasContext *ctx, int rm)
          return;
      }
  
-    /* The helper may raise ILLEGAL_INSN -- record binv for unwind. */
-    decode_save_opc(ctx);
      gen_helper_set_rounding_mode(cpu_env, tcg_constant_i32(rm));
  }
  
@@ -1055,6 +1051,7 @@ static void decode_opc(CPURISCVState *env, DisasContext *ctx, uint16_t opcode)
  
      /* Check for compressed insn */
      if (extract16(opcode, 0, 2) != 3) {
+        decode_save_opc(ctx, opcode);
          if (!has_ext(ctx, RVC)) {
              gen_exception_illegal(ctx);
          } else {
@@ -1071,6 +1068,7 @@ static void decode_opc(CPURISCVState *env, DisasContext 
*ctx, uint16_t opcode)
                                               ctx->base.pc_next + 2));
          ctx->opcode = opcode32;
          ctx->pc_succ_insn = ctx->base.pc_next + 4;
+        decode_save_opc(ctx, opcode32);
  
          for (size_t i = 0; i < ARRAY_SIZE(decoders); ++i) {
              if (decoders[i].guard_func(ctx) &&