RISC-V: Add support for Ztso

The Ztso extension is already ratified, this adds it as a CPU property
and adds various fences throughout the port in order to allow TSO
targets to function on weaker hosts.  We need no fences for AMOs as
they're already SC, the places we need barriers are described.
These fences are placed in the RISC-V backend rather than TCG as is
planned for x86-on-arm64 because RISC-V allows heterogeneous (and
likely soon dynamic) hart memory models.

Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Message-ID: <20240207122256.902627-2-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 71bdedc9bbfc55945b37fc2b08c2a95b64e6af91..37425e0e50cbb34a4f6072be322bc4d113d6de94 100644 (file)
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -149,6 +149,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
     ISA_EXT_DATA_ENTRY(zksed, PRIV_VERSION_1_12_0, ext_zksed),
     ISA_EXT_DATA_ENTRY(zksh, PRIV_VERSION_1_12_0, ext_zksh),
     ISA_EXT_DATA_ENTRY(zkt, PRIV_VERSION_1_12_0, ext_zkt),
+    ISA_EXT_DATA_ENTRY(ztso, PRIV_VERSION_1_12_0, ext_ztso),
     ISA_EXT_DATA_ENTRY(zvbb, PRIV_VERSION_1_12_0, ext_zvbb),
     ISA_EXT_DATA_ENTRY(zvbc, PRIV_VERSION_1_12_0, ext_zvbc),
     ISA_EXT_DATA_ENTRY(zve32f, PRIV_VERSION_1_10_0, ext_zve32f),
@@ -1500,6 +1501,7 @@ const RISCVCPUMultiExtConfig riscv_cpu_extensions[] = {
     MULTI_EXT_CFG_BOOL("zksed", ext_zksed, false),
     MULTI_EXT_CFG_BOOL("zksh", ext_zksh, false),
     MULTI_EXT_CFG_BOOL("zkt", ext_zkt, false),
+    MULTI_EXT_CFG_BOOL("ztso", ext_ztso, false),
 
     MULTI_EXT_CFG_BOOL("zdinx", ext_zdinx, false),
     MULTI_EXT_CFG_BOOL("zfinx", ext_zfinx, false),

diff --git a/target/riscv/cpu_cfg.h b/target/riscv/cpu_cfg.h
index be39870691ad1eada512ed2b5678efad26e9acf9..2040b90da0da8f600bca0d6cf461939852de62e1 100644 (file)
--- a/target/riscv/cpu_cfg.h
+++ b/target/riscv/cpu_cfg.h
@@ -71,6 +71,7 @@ struct RISCVCPUConfig {
     bool ext_zihintntl;
     bool ext_zihintpause;
     bool ext_zihpm;
+    bool ext_ztso;
     bool ext_smstateen;
     bool ext_sstc;
     bool ext_svadu;

diff --git a/target/riscv/insn_trans/trans_rva.c.inc b/target/riscv/insn_trans/trans_rva.c.inc
index 267930e5bc4e378cb67f6347b43ecb67b65f9371..4a9e4591d14cafec8d3c8590063834e7da4c299b 100644 (file)
--- a/target/riscv/insn_trans/trans_rva.c.inc
+++ b/target/riscv/insn_trans/trans_rva.c.inc
@@ -40,7 +40,11 @@ static bool gen_lr(DisasContext *ctx, arg_atomic *a, MemOp mop)
         tcg_gen_mb(TCG_MO_ALL | TCG_BAR_STRL);
     }
     tcg_gen_qemu_ld_tl(load_val, src1, ctx->mem_idx, mop);
-    if (a->aq) {
+    /*
+     * TSO defines AMOs as acquire+release-RCsc, but does not define LR/SC as
+     * AMOs.  Instead treat them like loads.
+     */
+    if (a->aq || ctx->ztso) {
         tcg_gen_mb(TCG_MO_ALL | TCG_BAR_LDAQ);
     }
 
@@ -76,9 +80,10 @@ static bool gen_sc(DisasContext *ctx, arg_atomic *a, MemOp mop)
     gen_set_label(l1);
     /*
      * Address comparison failure.  However, we still need to
-     * provide the memory barrier implied by AQ/RL.
+     * provide the memory barrier implied by AQ/RL/TSO.
      */
-    tcg_gen_mb(TCG_MO_ALL + a->aq * TCG_BAR_LDAQ + a->rl * TCG_BAR_STRL);
+    TCGBar bar_strl = (ctx->ztso || a->rl) ? TCG_BAR_STRL : 0;
+    tcg_gen_mb(TCG_MO_ALL + a->aq * TCG_BAR_LDAQ + bar_strl);
     gen_set_gpr(ctx, a->rd, tcg_constant_tl(1));
 
     gen_set_label(l2);

diff --git a/target/riscv/insn_trans/trans_rvi.c.inc b/target/riscv/insn_trans/trans_rvi.c.inc
index faf6d65064f06d2e99f1fdd6f96fb3fcc557179e..ad40d3e87f7fb5f7faee30f049785b05ed7aaceb 100644 (file)
--- a/target/riscv/insn_trans/trans_rvi.c.inc
+++ b/target/riscv/insn_trans/trans_rvi.c.inc
@@ -266,12 +266,20 @@ static bool gen_load_i128(DisasContext *ctx, arg_lb *a, MemOp memop)
 
 static bool gen_load(DisasContext *ctx, arg_lb *a, MemOp memop)
 {
+    bool out;
+
     decode_save_opc(ctx);
     if (get_xl(ctx) == MXL_RV128) {
-        return gen_load_i128(ctx, a, memop);
+        out = gen_load_i128(ctx, a, memop);
     } else {
-        return gen_load_tl(ctx, a, memop);
+        out = gen_load_tl(ctx, a, memop);
+    }
+
+    if (ctx->ztso) {
+        tcg_gen_mb(TCG_MO_ALL | TCG_BAR_LDAQ);
     }
+
+    return out;
 }
 
 static bool trans_lb(DisasContext *ctx, arg_lb *a)
@@ -328,6 +336,10 @@ static bool gen_store_tl(DisasContext *ctx, arg_sb *a, MemOp memop)
     TCGv addr = get_address(ctx, a->rs1, a->imm);
     TCGv data = get_gpr(ctx, a->rs2, EXT_NONE);
 
+    if (ctx->ztso) {
+        tcg_gen_mb(TCG_MO_ALL | TCG_BAR_STRL);
+    }
+
     tcg_gen_qemu_st_tl(data, addr, ctx->mem_idx, memop);
     return true;
 }

diff --git a/target/riscv/insn_trans/trans_rvv.c.inc b/target/riscv/insn_trans/trans_rvv.c.inc
index 9e101ab434359d615d5edcfc88c3dddffe93eaeb..742008f58b874c8f952cca117fa1cd12f10764c4 100644 (file)
--- a/target/riscv/insn_trans/trans_rvv.c.inc
+++ b/target/riscv/insn_trans/trans_rvv.c.inc
@@ -636,8 +636,28 @@ static bool ldst_us_trans(uint32_t vd, uint32_t rs1, uint32_t data,
     tcg_gen_addi_ptr(dest, tcg_env, vreg_ofs(s, vd));
     tcg_gen_addi_ptr(mask, tcg_env, vreg_ofs(s, 0));
 
+    /*
+     * According to the specification
+     *
+     *   Additionally, if the Ztso extension is implemented, then vector memory
+     *   instructions in the V extension and Zve family of extensions follow
+     *   RVTSO at the instruction level.  The Ztso extension does not
+     *   strengthen the ordering of intra-instruction element accesses.
+     *
+     * as a result neither ordered nor unordered accesses from the V
+     * instructions need ordering within the loop but we do still need barriers
+     * around the loop.
+     */
+    if (is_store && s->ztso) {
+        tcg_gen_mb(TCG_MO_ALL | TCG_BAR_STRL);
+    }
+
     fn(dest, mask, base, tcg_env, desc);
 
+    if (!is_store && s->ztso) {
+        tcg_gen_mb(TCG_MO_ALL | TCG_BAR_LDAQ);
+    }
+
     if (!is_store) {
         mark_vs_dirty(s);
     }

diff --git a/target/riscv/translate.c b/target/riscv/translate.c
index 177418b2b9e44cb7d8c9d93fdd5b0906d776a37f..ea5d52b2ef70a0c9f4febdc93555277ac0ed5e42 100644 (file)
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -109,6 +109,8 @@ typedef struct DisasContext {
     /* PointerMasking extension */
     bool pm_mask_enabled;
     bool pm_base_enabled;
+    /* Ztso */
+    bool ztso;
     /* Use icount trigger for native debug */
     bool itrigger;
     /* FRM is known to contain a valid value. */
@@ -1196,6 +1198,7 @@ static void riscv_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)
     ctx->cs = cs;
     ctx->pm_mask_enabled = FIELD_EX32(tb_flags, TB_FLAGS, PM_MASK_ENABLED);
     ctx->pm_base_enabled = FIELD_EX32(tb_flags, TB_FLAGS, PM_BASE_ENABLED);
+    ctx->ztso = cpu->cfg.ext_ztso;
     ctx->itrigger = FIELD_EX32(tb_flags, TB_FLAGS, ITRIGGER);
     ctx->zero = tcg_constant_tl(0);
     ctx->virt_inst_excp = false;