[PATCH v7 00/10] make write_misa a no-op and FEATURE_* cleanups

[PATCH v7 00/10] make write_misa a no-op and FEATURE_* cleanups

[Daniel Henrique Barboza]

Hi,

In this version we gave up removing all the write_misa() body and,
instead, we went back to something closer to what we were doing in v2.
write_misa() is now gated behind an experimental x-misa-w cfg option,
defaulted to false.

The idea is that x-misa-w allow us to keep experimenting and testing the
code. Marking it as experimental will (hopefully) make users wary of the
fact that this feature is unstable. The expectation is that the flag will
be removed once write_misa() is ready to always write MISA.

Changes from v6:
- patches without reviews/acks: patch 3
- patch 2: taken from version 3, acks and r-bs preserved
- patch 3:
  - rename 'misa-w' to 'x-misa-w' to be clearer about our intents with
    the cfg option
- v6 link: https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05047.html

Daniel Henrique Barboza (10):
  target/riscv: introduce riscv_cpu_cfg()
  target/riscv: do not mask unsupported QEMU extensions in write_misa()
  target/riscv: allow MISA writes as experimental
  target/riscv: remove RISCV_FEATURE_DEBUG
  target/riscv/cpu.c: error out if EPMP is enabled without PMP
  target/riscv: remove RISCV_FEATURE_EPMP
  target/riscv: remove RISCV_FEATURE_PMP
  hw/riscv/virt.c: do not use RISCV_FEATURE_MMU in
    create_fdt_socket_cpus()
  target/riscv: remove RISCV_FEATURE_MMU
  target/riscv/cpu: remove CPUArchState::features and friends

 hw/riscv/virt.c           |  7 ++++---
 target/riscv/cpu.c        | 25 ++++++++++---------------
 target/riscv/cpu.h        | 29 ++++++-----------------------
 target/riscv/cpu_helper.c |  6 +++---
 target/riscv/csr.c        | 15 ++++++---------
 target/riscv/machine.c    | 11 ++++-------
 target/riscv/monitor.c    |  2 +-
 target/riscv/op_helper.c  |  2 +-
 target/riscv/pmp.c        |  8 ++++----
 9 files changed, 39 insertions(+), 66 deletions(-)

-- 
2.39.2

[PATCH v7 01/10] target/riscv: introduce riscv_cpu_cfg()

[Daniel Henrique Barboza]

We're going to do changes that requires accessing the RISCVCPUConfig
struct from the RISCVCPU, having access only to a CPURISCVState 'env'
pointer. Add a helper to make the code easier to read.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/riscv/cpu.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 7128438d8e..215423499e 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -654,6 +654,11 @@ static inline RISCVMXL riscv_cpu_mxl(CPURISCVState *env)
 #endif
 #define riscv_cpu_mxl_bits(env) (1UL << (4 + riscv_cpu_mxl(env)))
 
+static inline const RISCVCPUConfig *riscv_cpu_cfg(CPURISCVState *env)
+{
+    return &env_archcpu(env)->cfg;
+}
+
 #if defined(TARGET_RISCV32)
 #define cpu_recompute_xl(env)  ((void)(env), MXL_RV32)
 #else
-- 
2.39.2

[PATCH v7 02/10] target/riscv: do not mask unsupported QEMU extensions in write_misa()

[Daniel Henrique Barboza]

The masking done using env->misa_ext_mask already filters any extension
that QEMU doesn't support. If the hart supports the extension then QEMU
supports it as well.

If the masking done by env->misa_ext_mask is somehow letting unsupported
QEMU extensions pass by, misa_ext_mask itself needs to be fixed instead.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
---
 target/riscv/csr.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 1b0a0c1693..e149b453da 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -1356,9 +1356,6 @@ static RISCVException write_misa(CPURISCVState *env, int csrno,
     /* Mask extensions that are not supported by this hart */
     val &= env->misa_ext_mask;
 
-    /* Mask extensions that are not supported by QEMU */
-    val &= (RVI | RVE | RVM | RVA | RVF | RVD | RVC | RVS | RVU | RVV);
-
     /* 'D' depends on 'F', so clear 'D' if 'F' is not present */
     if ((val & RVD) && !(val & RVF)) {
         val &= ~RVD;
-- 
2.39.2

[PATCH v7 03/10] target/riscv: allow MISA writes as experimental

[Daniel Henrique Barboza]

At this moment, and apparently since ever, we have no way of enabling
RISCV_FEATURE_MISA. This means that all the code from write_misa(), all
the nuts and bolts that handles how to properly write this CSR, has
always been a no-op as well because write_misa() will always exit
earlier.

This seems to be benign in the majority of cases. Booting an Ubuntu
'virt' guest and logging all the calls to 'write_misa' shows that no
writes to MISA CSR was attempted. Writing MISA, i.e. enabling/disabling
RISC-V extensions after the machine is powered on, seems to be a niche
use.

After discussions in the mailing list, most notably in [1], we reached
the consensus that this code is not suited to be exposed to users
because it's not well tested, but at the same time removing it is a bit
extreme because we would like to fix it, and it's easier to do so with
the code available to use instead of fetching it from git log.

The approach taken here is to get rid of RISCV_FEATURE_MISA altogether
and use a new experimental flag called x-misa-w. The default value is
false, meaning that we're keeping the existing behavior of doing nothing
if a write_misa() is attempted. As with any existing experimental flag,
x-misa-w is also a temporary flag that we need to remove once we fix
write_misa().

[1] https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05092.html

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 target/riscv/cpu.c | 6 ++++++
 target/riscv/cpu.h | 2 +-
 target/riscv/csr.c | 2 +-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 93b52b826c..1d637b1acd 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -1210,6 +1210,12 @@ static Property riscv_cpu_properties[] = {
 
     DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
     DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
+
+    /*
+     * write_misa() is marked as experimental for now so mark
+     * it with -x and default to 'false'.
+     */
+    DEFINE_PROP_BOOL("x-misa-w", RISCVCPU, cfg.misa_w, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 215423499e..9d3304bcda 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -89,7 +89,6 @@ enum {
     RISCV_FEATURE_MMU,
     RISCV_FEATURE_PMP,
     RISCV_FEATURE_EPMP,
-    RISCV_FEATURE_MISA,
     RISCV_FEATURE_DEBUG
 };
 
@@ -498,6 +497,7 @@ struct RISCVCPUConfig {
     bool pmp;
     bool epmp;
     bool debug;
+    bool misa_w;
 
     bool short_isa_string;
 };
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index e149b453da..3cb8d2ffad 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -1329,7 +1329,7 @@ static RISCVException read_misa(CPURISCVState *env, int csrno,
 static RISCVException write_misa(CPURISCVState *env, int csrno,
                                  target_ulong val)
 {
-    if (!riscv_feature(env, RISCV_FEATURE_MISA)) {
+    if (!riscv_cpu_cfg(env)->misa_w) {
         /* drop write to misa */
         return RISCV_EXCP_NONE;
     }
-- 
2.39.2

[PATCH v7 04/10] target/riscv: remove RISCV_FEATURE_DEBUG

[Daniel Henrique Barboza]

RISCV_FEATURE_DEBUG will always follow the value defined by
cpu->cfg.debug flag. Read the flag instead.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
---
 target/riscv/cpu.c        | 6 +-----
 target/riscv/cpu.h        | 1 -
 target/riscv/cpu_helper.c | 2 +-
 target/riscv/csr.c        | 2 +-
 target/riscv/machine.c    | 3 +--
 5 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 1d637b1acd..13e55ec5bd 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -637,7 +637,7 @@ static void riscv_cpu_reset_hold(Object *obj)
     set_default_nan_mode(1, &env->fp_status);
 
 #ifndef CONFIG_USER_ONLY
-    if (riscv_feature(env, RISCV_FEATURE_DEBUG)) {
+    if (cpu->cfg.debug) {
         riscv_trigger_init(env);
     }
 
@@ -935,10 +935,6 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
         }
     }
 
-    if (cpu->cfg.debug) {
-        riscv_set_feature(env, RISCV_FEATURE_DEBUG);
-    }
-
 
 #ifndef CONFIG_USER_ONLY
     if (cpu->cfg.ext_sstc) {
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 9d3304bcda..5295c2d701 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -89,7 +89,6 @@ enum {
     RISCV_FEATURE_MMU,
     RISCV_FEATURE_PMP,
     RISCV_FEATURE_EPMP,
-    RISCV_FEATURE_DEBUG
 };
 
 /* Privileged specification version */
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index ad8d82662c..4cdd247c6c 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -105,7 +105,7 @@ void cpu_get_tb_cpu_state(CPURISCVState *env, target_ulong *pc,
         flags = FIELD_DP32(flags, TB_FLAGS, MSTATUS_HS_VS,
                            get_field(env->mstatus_hs, MSTATUS_VS));
     }
-    if (riscv_feature(env, RISCV_FEATURE_DEBUG) && !icount_enabled()) {
+    if (cpu->cfg.debug && !icount_enabled()) {
         flags = FIELD_DP32(flags, TB_FLAGS, ITRIGGER, env->itrigger_enabled);
     }
 #endif
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 3cb8d2ffad..e220c4a5fd 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -437,7 +437,7 @@ static RISCVException epmp(CPURISCVState *env, int csrno)
 
 static RISCVException debug(CPURISCVState *env, int csrno)
 {
-    if (riscv_feature(env, RISCV_FEATURE_DEBUG)) {
+    if (riscv_cpu_cfg(env)->debug) {
         return RISCV_EXCP_NONE;
     }
 
diff --git a/target/riscv/machine.c b/target/riscv/machine.c
index c6ce318cce..4634968898 100644
--- a/target/riscv/machine.c
+++ b/target/riscv/machine.c
@@ -226,9 +226,8 @@ static const VMStateDescription vmstate_kvmtimer = {
 static bool debug_needed(void *opaque)
 {
     RISCVCPU *cpu = opaque;
-    CPURISCVState *env = &cpu->env;
 
-    return riscv_feature(env, RISCV_FEATURE_DEBUG);
+    return cpu->cfg.debug;
 }
 
 static int debug_post_load(void *opaque, int version_id)
-- 
2.39.2

[PATCH v7 05/10] target/riscv/cpu.c: error out if EPMP is enabled without PMP

[Daniel Henrique Barboza]

Instead of silently ignoring the EPMP setting if there is no PMP
available, error out informing the user that EPMP depends on PMP
support:

$ ./qemu-system-riscv64 -cpu rv64,pmp=false,x-epmp=true
qemu-system-riscv64: Invalid configuration: EPMP requires PMP support

This will force users to pick saner options in the QEMU command line.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
---
 target/riscv/cpu.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 13e55ec5bd..aec7830c44 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -925,13 +925,18 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
 
     if (cpu->cfg.pmp) {
         riscv_set_feature(env, RISCV_FEATURE_PMP);
+    }
+
+    if (cpu->cfg.epmp) {
+        riscv_set_feature(env, RISCV_FEATURE_EPMP);
 
         /*
          * Enhanced PMP should only be available
          * on harts with PMP support
          */
-        if (cpu->cfg.epmp) {
-            riscv_set_feature(env, RISCV_FEATURE_EPMP);
+        if (!cpu->cfg.pmp) {
+            error_setg(errp, "Invalid configuration: EPMP requires PMP support");
+            return;
         }
     }
 
-- 
2.39.2

[PATCH v7 06/10] target/riscv: remove RISCV_FEATURE_EPMP

[Daniel Henrique Barboza]

RISCV_FEATURE_EPMP is always set to the same value as the cpu->cfg.epmp
flag. Use the flag directly.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
---
 target/riscv/cpu.c | 10 +++-------
 target/riscv/cpu.h |  1 -
 target/riscv/csr.c |  2 +-
 target/riscv/pmp.c |  4 ++--
 4 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index aec7830c44..807a466f34 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -927,17 +927,13 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
         riscv_set_feature(env, RISCV_FEATURE_PMP);
     }
 
-    if (cpu->cfg.epmp) {
-        riscv_set_feature(env, RISCV_FEATURE_EPMP);
-
+    if (cpu->cfg.epmp && !cpu->cfg.pmp) {
         /*
          * Enhanced PMP should only be available
          * on harts with PMP support
          */
-        if (!cpu->cfg.pmp) {
-            error_setg(errp, "Invalid configuration: EPMP requires PMP support");
-            return;
-        }
+        error_setg(errp, "Invalid configuration: EPMP requires PMP support");
+        return;
     }
 
 
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 5295c2d701..d4da420912 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -88,7 +88,6 @@
 enum {
     RISCV_FEATURE_MMU,
     RISCV_FEATURE_PMP,
-    RISCV_FEATURE_EPMP,
 };
 
 /* Privileged specification version */
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index e220c4a5fd..951327022d 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -428,7 +428,7 @@ static RISCVException pmp(CPURISCVState *env, int csrno)
 
 static RISCVException epmp(CPURISCVState *env, int csrno)
 {
-    if (env->priv == PRV_M && riscv_feature(env, RISCV_FEATURE_EPMP)) {
+    if (env->priv == PRV_M && riscv_cpu_cfg(env)->epmp) {
         return RISCV_EXCP_NONE;
     }
 
diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index 4bc4113531..aa4d1996e9 100644
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -88,7 +88,7 @@ static void pmp_write_cfg(CPURISCVState *env, uint32_t pmp_index, uint8_t val)
     if (pmp_index < MAX_RISCV_PMPS) {
         bool locked = true;
 
-        if (riscv_feature(env, RISCV_FEATURE_EPMP)) {
+        if (riscv_cpu_cfg(env)->epmp) {
             /* mseccfg.RLB is set */
             if (MSECCFG_RLB_ISSET(env)) {
                 locked = false;
@@ -239,7 +239,7 @@ static bool pmp_hart_has_privs_default(CPURISCVState *env, target_ulong addr,
 {
     bool ret;
 
-    if (riscv_feature(env, RISCV_FEATURE_EPMP)) {
+    if (riscv_cpu_cfg(env)->epmp) {
         if (MSECCFG_MMWP_ISSET(env)) {
             /*
              * The Machine Mode Whitelist Policy (mseccfg.MMWP) is set
-- 
2.39.2

[PATCH v7 07/10] target/riscv: remove RISCV_FEATURE_PMP

[Daniel Henrique Barboza]

RISCV_FEATURE_PMP is being set via riscv_set_feature() by mirroring the
cpu->cfg.pmp flag. Use the flag instead.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
---
 target/riscv/cpu.c        | 4 ----
 target/riscv/cpu.h        | 1 -
 target/riscv/cpu_helper.c | 2 +-
 target/riscv/csr.c        | 2 +-
 target/riscv/machine.c    | 3 +--
 target/riscv/op_helper.c  | 2 +-
 target/riscv/pmp.c        | 2 +-
 7 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 807a466f34..d321ad28d2 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -923,10 +923,6 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
         riscv_set_feature(env, RISCV_FEATURE_MMU);
     }
 
-    if (cpu->cfg.pmp) {
-        riscv_set_feature(env, RISCV_FEATURE_PMP);
-    }
-
     if (cpu->cfg.epmp && !cpu->cfg.pmp) {
         /*
          * Enhanced PMP should only be available
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index d4da420912..3246153db2 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -87,7 +87,6 @@
    so a cpu features bitfield is required, likewise for optional PMP support */
 enum {
     RISCV_FEATURE_MMU,
-    RISCV_FEATURE_PMP,
 };
 
 /* Privileged specification version */
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 4cdd247c6c..292b6b3168 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -706,7 +706,7 @@ static int get_physical_address_pmp(CPURISCVState *env, int *prot,
     pmp_priv_t pmp_priv;
     int pmp_index = -1;
 
-    if (!riscv_feature(env, RISCV_FEATURE_PMP)) {
+    if (!riscv_cpu_cfg(env)->pmp) {
         *prot = PAGE_READ | PAGE_WRITE | PAGE_EXEC;
         return TRANSLATE_SUCCESS;
     }
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 951327022d..cf33494945 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -419,7 +419,7 @@ static int aia_hmode32(CPURISCVState *env, int csrno)
 
 static RISCVException pmp(CPURISCVState *env, int csrno)
 {
-    if (riscv_feature(env, RISCV_FEATURE_PMP)) {
+    if (riscv_cpu_cfg(env)->pmp) {
         return RISCV_EXCP_NONE;
     }
 
diff --git a/target/riscv/machine.c b/target/riscv/machine.c
index 4634968898..67e9e56853 100644
--- a/target/riscv/machine.c
+++ b/target/riscv/machine.c
@@ -27,9 +27,8 @@
 static bool pmp_needed(void *opaque)
 {
     RISCVCPU *cpu = opaque;
-    CPURISCVState *env = &cpu->env;
 
-    return riscv_feature(env, RISCV_FEATURE_PMP);
+    return cpu->cfg.pmp;
 }
 
 static int pmp_post_load(void *opaque, int version_id)
diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
index 48f918b71b..9c0b91c88f 100644
--- a/target/riscv/op_helper.c
+++ b/target/riscv/op_helper.c
@@ -195,7 +195,7 @@ target_ulong helper_mret(CPURISCVState *env)
     uint64_t mstatus = env->mstatus;
     target_ulong prev_priv = get_field(mstatus, MSTATUS_MPP);
 
-    if (riscv_feature(env, RISCV_FEATURE_PMP) &&
+    if (riscv_cpu_cfg(env)->pmp &&
         !pmp_get_num_rules(env) && (prev_priv != PRV_M)) {
         riscv_raise_exception(env, RISCV_EXCP_INST_ACCESS_FAULT, GETPC());
     }
diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index aa4d1996e9..205bfbe090 100644
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -265,7 +265,7 @@ static bool pmp_hart_has_privs_default(CPURISCVState *env, target_ulong addr,
         }
     }
 
-    if ((!riscv_feature(env, RISCV_FEATURE_PMP)) || (mode == PRV_M)) {
+    if (!riscv_cpu_cfg(env)->pmp || (mode == PRV_M)) {
         /*
          * Privileged spec v1.10 states if HW doesn't implement any PMP entry
          * or no PMP entry matches an M-Mode access, the access succeeds.
-- 
2.39.2

[PATCH v7 08/10] hw/riscv/virt.c: do not use RISCV_FEATURE_MMU in create_fdt_socket_cpus()

[Daniel Henrique Barboza]

Read cpu_ptr->cfg.mmu directly. As a bonus, use cpu_ptr in
riscv_isa_string().

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
---
 hw/riscv/virt.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
index 86c4adc0c9..49f2c157f7 100644
--- a/hw/riscv/virt.c
+++ b/hw/riscv/virt.c
@@ -232,20 +232,21 @@ static void create_fdt_socket_cpus(RISCVVirtState *s, int socket,
     bool is_32_bit = riscv_is_32bit(&s->soc[0]);
 
     for (cpu = s->soc[socket].num_harts - 1; cpu >= 0; cpu--) {
+        RISCVCPU *cpu_ptr = &s->soc[socket].harts[cpu];
+
         cpu_phandle = (*phandle)++;
 
         cpu_name = g_strdup_printf("/cpus/cpu@%d",
             s->soc[socket].hartid_base + cpu);
         qemu_fdt_add_subnode(ms->fdt, cpu_name);
-        if (riscv_feature(&s->soc[socket].harts[cpu].env,
-                          RISCV_FEATURE_MMU)) {
+        if (cpu_ptr->cfg.mmu) {
             qemu_fdt_setprop_string(ms->fdt, cpu_name, "mmu-type",
                                     (is_32_bit) ? "riscv,sv32" : "riscv,sv48");
         } else {
             qemu_fdt_setprop_string(ms->fdt, cpu_name, "mmu-type",
                                     "riscv,none");
         }
-        name = riscv_isa_string(&s->soc[socket].harts[cpu]);
+        name = riscv_isa_string(cpu_ptr);
         qemu_fdt_setprop_string(ms->fdt, cpu_name, "riscv,isa", name);
         g_free(name);
         qemu_fdt_setprop_string(ms->fdt, cpu_name, "compatible", "riscv");
-- 
2.39.2

[PATCH v7 09/10] target/riscv: remove RISCV_FEATURE_MMU

[Daniel Henrique Barboza]

RISCV_FEATURE_MMU is set whether cpu->cfg.mmu is set, so let's just use
the flag directly instead.

With this change the enum is also removed. It is worth noticing that
this enum, and all the RISCV_FEATURES_* that were contained in it,
predates the existence of the cpu->cfg object. Today, using cpu->cfg is
an easier way to retrieve all the features and extensions enabled in the
hart.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
---
 target/riscv/cpu.c        | 4 ----
 target/riscv/cpu.h        | 7 -------
 target/riscv/cpu_helper.c | 2 +-
 target/riscv/csr.c        | 4 ++--
 target/riscv/monitor.c    | 2 +-
 target/riscv/pmp.c        | 2 +-
 6 files changed, 5 insertions(+), 16 deletions(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index d321ad28d2..11da920915 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -919,10 +919,6 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
         }
     }
 
-    if (cpu->cfg.mmu) {
-        riscv_set_feature(env, RISCV_FEATURE_MMU);
-    }
-
     if (cpu->cfg.epmp && !cpu->cfg.pmp) {
         /*
          * Enhanced PMP should only be available
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 3246153db2..fb0f2afe0d 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -81,13 +81,6 @@
 #define RVH RV('H')
 #define RVJ RV('J')
 
-/* S extension denotes that Supervisor mode exists, however it is possible
-   to have a core that support S mode but does not have an MMU and there
-   is currently no bit in misa to indicate whether an MMU exists or not
-   so a cpu features bitfield is required, likewise for optional PMP support */
-enum {
-    RISCV_FEATURE_MMU,
-};
 
 /* Privileged specification version */
 enum {
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 292b6b3168..eda2293470 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -796,7 +796,7 @@ static int get_physical_address(CPURISCVState *env, hwaddr *physical,
         mode = PRV_U;
     }
 
-    if (mode == PRV_M || !riscv_feature(env, RISCV_FEATURE_MMU)) {
+    if (mode == PRV_M || !riscv_cpu_cfg(env)->mmu) {
         *physical = addr;
         *prot = PAGE_READ | PAGE_WRITE | PAGE_EXEC;
         return TRANSLATE_SUCCESS;
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index cf33494945..75a540bfcb 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -2621,7 +2621,7 @@ static RISCVException rmw_siph(CPURISCVState *env, int csrno,
 static RISCVException read_satp(CPURISCVState *env, int csrno,
                                 target_ulong *val)
 {
-    if (!riscv_feature(env, RISCV_FEATURE_MMU)) {
+    if (!riscv_cpu_cfg(env)->mmu) {
         *val = 0;
         return RISCV_EXCP_NONE;
     }
@@ -2640,7 +2640,7 @@ static RISCVException write_satp(CPURISCVState *env, int csrno,
 {
     target_ulong vm, mask;
 
-    if (!riscv_feature(env, RISCV_FEATURE_MMU)) {
+    if (!riscv_cpu_cfg(env)->mmu) {
         return RISCV_EXCP_NONE;
     }
 
diff --git a/target/riscv/monitor.c b/target/riscv/monitor.c
index 236f93b9f5..f36ddfa967 100644
--- a/target/riscv/monitor.c
+++ b/target/riscv/monitor.c
@@ -218,7 +218,7 @@ void hmp_info_mem(Monitor *mon, const QDict *qdict)
         return;
     }
 
-    if (!riscv_feature(env, RISCV_FEATURE_MMU)) {
+    if (!riscv_cpu_cfg(env)->mmu) {
         monitor_printf(mon, "S-mode MMU unavailable\n");
         return;
     }
diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index 205bfbe090..a08cd95658 100644
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -315,7 +315,7 @@ int pmp_hart_has_privs(CPURISCVState *env, target_ulong addr,
     }
 
     if (size == 0) {
-        if (riscv_feature(env, RISCV_FEATURE_MMU)) {
+        if (riscv_cpu_cfg(env)->mmu) {
             /*
              * If size is unknown (0), assume that all bytes
              * from addr to the end of the page will be accessed.
-- 
2.39.2

[PATCH v7 10/10] target/riscv/cpu: remove CPUArchState::features and friends

[Daniel Henrique Barboza]

The attribute is no longer used since we can retrieve all the enabled
features in the hart by using cpu->cfg instead.

Remove env->feature, riscv_feature() and riscv_set_feature(). We also
need to bump vmstate_riscv_cpu version_id and minimal_version_id since
'features' is no longer being migrated.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
---
 target/riscv/cpu.h     | 12 ------------
 target/riscv/machine.c |  5 ++---
 2 files changed, 2 insertions(+), 15 deletions(-)

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index fb0f2afe0d..29a12acac1 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -173,8 +173,6 @@ struct CPUArchState {
     /* 128-bit helpers upper part return value */
     target_ulong retxh;
 
-    uint32_t features;
-
 #ifdef CONFIG_USER_ONLY
     uint32_t elf_flags;
 #endif
@@ -525,16 +523,6 @@ static inline int riscv_has_ext(CPURISCVState *env, target_ulong ext)
     return (env->misa_ext & ext) != 0;
 }
 
-static inline bool riscv_feature(CPURISCVState *env, int feature)
-{
-    return env->features & (1ULL << feature);
-}
-
-static inline void riscv_set_feature(CPURISCVState *env, int feature)
-{
-    env->features |= (1ULL << feature);
-}
-
 #include "cpu_user.h"
 
 extern const char * const riscv_int_regnames[];
diff --git a/target/riscv/machine.c b/target/riscv/machine.c
index 67e9e56853..9c455931d8 100644
--- a/target/riscv/machine.c
+++ b/target/riscv/machine.c
@@ -331,8 +331,8 @@ static const VMStateDescription vmstate_pmu_ctr_state = {
 
 const VMStateDescription vmstate_riscv_cpu = {
     .name = "cpu",
-    .version_id = 6,
-    .minimum_version_id = 6,
+    .version_id = 7,
+    .minimum_version_id = 7,
     .post_load = riscv_cpu_post_load,
     .fields = (VMStateField[]) {
         VMSTATE_UINTTL_ARRAY(env.gpr, RISCVCPU, 32),
@@ -351,7 +351,6 @@ const VMStateDescription vmstate_riscv_cpu = {
         VMSTATE_UINT32(env.misa_ext, RISCVCPU),
         VMSTATE_UINT32(env.misa_mxl_max, RISCVCPU),
         VMSTATE_UINT32(env.misa_ext_mask, RISCVCPU),
-        VMSTATE_UINT32(env.features, RISCVCPU),
         VMSTATE_UINTTL(env.priv, RISCVCPU),
         VMSTATE_UINTTL(env.virt, RISCVCPU),
         VMSTATE_UINT64(env.resetvec, RISCVCPU),
-- 
2.39.2

Re: [PATCH v7 03/10] target/riscv: allow MISA writes as experimental

[liweiwei]

On 2023/2/23 02:51, Daniel Henrique Barboza wrote:
> At this moment, and apparently since ever, we have no way of enabling
> RISCV_FEATURE_MISA. This means that all the code from write_misa(), all
> the nuts and bolts that handles how to properly write this CSR, has
> always been a no-op as well because write_misa() will always exit
> earlier.
>
> This seems to be benign in the majority of cases. Booting an Ubuntu
> 'virt' guest and logging all the calls to 'write_misa' shows that no
> writes to MISA CSR was attempted. Writing MISA, i.e. enabling/disabling
> RISC-V extensions after the machine is powered on, seems to be a niche
> use.
>
> After discussions in the mailing list, most notably in [1], we reached
> the consensus that this code is not suited to be exposed to users
> because it's not well tested, but at the same time removing it is a bit
> extreme because we would like to fix it, and it's easier to do so with
> the code available to use instead of fetching it from git log.
>
> The approach taken here is to get rid of RISCV_FEATURE_MISA altogether
> and use a new experimental flag called x-misa-w. The default value is
> false, meaning that we're keeping the existing behavior of doing nothing
> if a write_misa() is attempted. As with any existing experimental flag,
> x-misa-w is also a temporary flag that we need to remove once we fix
> write_misa().
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05092.html
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

Acceptable to me.

Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>

Weiwei Li

> ---
>   target/riscv/cpu.c | 6 ++++++
>   target/riscv/cpu.h | 2 +-
>   target/riscv/csr.c | 2 +-
>   3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 93b52b826c..1d637b1acd 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -1210,6 +1210,12 @@ static Property riscv_cpu_properties[] = {
>   
>       DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
>       DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
> +
> +    /*
> +     * write_misa() is marked as experimental for now so mark
> +     * it with -x and default to 'false'.
> +     */
> +    DEFINE_PROP_BOOL("x-misa-w", RISCVCPU, cfg.misa_w, false),
>       DEFINE_PROP_END_OF_LIST(),
>   };
>   
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 215423499e..9d3304bcda 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -89,7 +89,6 @@ enum {
>       RISCV_FEATURE_MMU,
>       RISCV_FEATURE_PMP,
>       RISCV_FEATURE_EPMP,
> -    RISCV_FEATURE_MISA,
>       RISCV_FEATURE_DEBUG
>   };
>   
> @@ -498,6 +497,7 @@ struct RISCVCPUConfig {
>       bool pmp;
>       bool epmp;
>       bool debug;
> +    bool misa_w;
>   
>       bool short_isa_string;
>   };
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index e149b453da..3cb8d2ffad 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -1329,7 +1329,7 @@ static RISCVException read_misa(CPURISCVState *env, int csrno,
>   static RISCVException write_misa(CPURISCVState *env, int csrno,
>                                    target_ulong val)
>   {
> -    if (!riscv_feature(env, RISCV_FEATURE_MISA)) {
> +    if (!riscv_cpu_cfg(env)->misa_w) {
>           /* drop write to misa */
>           return RISCV_EXCP_NONE;
>       }

Re: [PATCH v7 03/10] target/riscv: allow MISA writes as experimental

[Andrew Jones]

On Wed, Feb 22, 2023 at 03:51:58PM -0300, Daniel Henrique Barboza wrote:
> At this moment, and apparently since ever, we have no way of enabling
> RISCV_FEATURE_MISA. This means that all the code from write_misa(), all
> the nuts and bolts that handles how to properly write this CSR, has
> always been a no-op as well because write_misa() will always exit
> earlier.
> 
> This seems to be benign in the majority of cases. Booting an Ubuntu
> 'virt' guest and logging all the calls to 'write_misa' shows that no
> writes to MISA CSR was attempted. Writing MISA, i.e. enabling/disabling
> RISC-V extensions after the machine is powered on, seems to be a niche
> use.
> 
> After discussions in the mailing list, most notably in [1], we reached
> the consensus that this code is not suited to be exposed to users
> because it's not well tested, but at the same time removing it is a bit
> extreme because we would like to fix it, and it's easier to do so with
> the code available to use instead of fetching it from git log.
> 
> The approach taken here is to get rid of RISCV_FEATURE_MISA altogether
> and use a new experimental flag called x-misa-w. The default value is
> false, meaning that we're keeping the existing behavior of doing nothing
> if a write_misa() is attempted. As with any existing experimental flag,
> x-misa-w is also a temporary flag that we need to remove once we fix
> write_misa().
> 
> [1] https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05092.html
> 
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>  target/riscv/cpu.c | 6 ++++++
>  target/riscv/cpu.h | 2 +-
>  target/riscv/csr.c | 2 +-
>  3 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 93b52b826c..1d637b1acd 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -1210,6 +1210,12 @@ static Property riscv_cpu_properties[] = {
>  
>      DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
>      DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
> +
> +    /*
> +     * write_misa() is marked as experimental for now so mark
> +     * it with -x and default to 'false'.
> +     */
> +    DEFINE_PROP_BOOL("x-misa-w", RISCVCPU, cfg.misa_w, false),
>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 215423499e..9d3304bcda 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -89,7 +89,6 @@ enum {
>      RISCV_FEATURE_MMU,
>      RISCV_FEATURE_PMP,
>      RISCV_FEATURE_EPMP,
> -    RISCV_FEATURE_MISA,
>      RISCV_FEATURE_DEBUG
>  };
>  
> @@ -498,6 +497,7 @@ struct RISCVCPUConfig {
>      bool pmp;
>      bool epmp;
>      bool debug;
> +    bool misa_w;
>  
>      bool short_isa_string;
>  };
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index e149b453da..3cb8d2ffad 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -1329,7 +1329,7 @@ static RISCVException read_misa(CPURISCVState *env, int csrno,
>  static RISCVException write_misa(CPURISCVState *env, int csrno,
>                                   target_ulong val)
>  {
> -    if (!riscv_feature(env, RISCV_FEATURE_MISA)) {
> +    if (!riscv_cpu_cfg(env)->misa_w) {
>          /* drop write to misa */
>          return RISCV_EXCP_NONE;
>      }
> -- 
> 2.39.2
> 
>

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Re: [PATCH v7 03/10] target/riscv: allow MISA writes as experimental

[Bin Meng]

On Thu, Feb 23, 2023 at 2:53 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> At this moment, and apparently since ever, we have no way of enabling
> RISCV_FEATURE_MISA. This means that all the code from write_misa(), all
> the nuts and bolts that handles how to properly write this CSR, has
> always been a no-op as well because write_misa() will always exit
> earlier.
>
> This seems to be benign in the majority of cases. Booting an Ubuntu
> 'virt' guest and logging all the calls to 'write_misa' shows that no
> writes to MISA CSR was attempted. Writing MISA, i.e. enabling/disabling
> RISC-V extensions after the machine is powered on, seems to be a niche
> use.
>
> After discussions in the mailing list, most notably in [1], we reached
> the consensus that this code is not suited to be exposed to users
> because it's not well tested, but at the same time removing it is a bit
> extreme because we would like to fix it, and it's easier to do so with
> the code available to use instead of fetching it from git log.
>
> The approach taken here is to get rid of RISCV_FEATURE_MISA altogether
> and use a new experimental flag called x-misa-w. The default value is
> false, meaning that we're keeping the existing behavior of doing nothing
> if a write_misa() is attempted. As with any existing experimental flag,
> x-misa-w is also a temporary flag that we need to remove once we fix
> write_misa().
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05092.html
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>  target/riscv/cpu.c | 6 ++++++
>  target/riscv/cpu.h | 2 +-
>  target/riscv/csr.c | 2 +-
>  3 files changed, 8 insertions(+), 2 deletions(-)
>

Reviewed-by: Bin Meng <bmeng@tinylab.org>

Re: [PATCH v7 03/10] target/riscv: allow MISA writes as experimental

[liweiwei]

On 2023/2/23 02:51, Daniel Henrique Barboza wrote:
> At this moment, and apparently since ever, we have no way of enabling
> RISCV_FEATURE_MISA. This means that all the code from write_misa(), all
> the nuts and bolts that handles how to properly write this CSR, has
> always been a no-op as well because write_misa() will always exit
> earlier.
>
> This seems to be benign in the majority of cases. Booting an Ubuntu
> 'virt' guest and logging all the calls to 'write_misa' shows that no
> writes to MISA CSR was attempted. Writing MISA, i.e. enabling/disabling
> RISC-V extensions after the machine is powered on, seems to be a niche
> use.
>
> After discussions in the mailing list, most notably in [1], we reached
> the consensus that this code is not suited to be exposed to users
> because it's not well tested, but at the same time removing it is a bit
> extreme because we would like to fix it, and it's easier to do so with
> the code available to use instead of fetching it from git log.
>
> The approach taken here is to get rid of RISCV_FEATURE_MISA altogether
> and use a new experimental flag called x-misa-w. The default value is
> false, meaning that we're keeping the existing behavior of doing nothing
> if a write_misa() is attempted. As with any existing experimental flag,
> x-misa-w is also a temporary flag that we need to remove once we fix
> write_misa().
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05092.html
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Weiwei Li<liweiwei@iscas.ac.cn>

Weiwei Li
> ---
>   target/riscv/cpu.c | 6 ++++++
>   target/riscv/cpu.h | 2 +-
>   target/riscv/csr.c | 2 +-
>   3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 93b52b826c..1d637b1acd 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -1210,6 +1210,12 @@ static Property riscv_cpu_properties[] = {
>   
>       DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
>       DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
> +
> +    /*
> +     * write_misa() is marked as experimental for now so mark
> +     * it with -x and default to 'false'.
> +     */
> +    DEFINE_PROP_BOOL("x-misa-w", RISCVCPU, cfg.misa_w, false),
>       DEFINE_PROP_END_OF_LIST(),
>   };
>   
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 215423499e..9d3304bcda 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -89,7 +89,6 @@ enum {
>       RISCV_FEATURE_MMU,
>       RISCV_FEATURE_PMP,
>       RISCV_FEATURE_EPMP,
> -    RISCV_FEATURE_MISA,
>       RISCV_FEATURE_DEBUG
>   };
>   
> @@ -498,6 +497,7 @@ struct RISCVCPUConfig {
>       bool pmp;
>       bool epmp;
>       bool debug;
> +    bool misa_w;
>   
>       bool short_isa_string;
>   };
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index e149b453da..3cb8d2ffad 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -1329,7 +1329,7 @@ static RISCVException read_misa(CPURISCVState *env, int csrno,
>   static RISCVException write_misa(CPURISCVState *env, int csrno,
>                                    target_ulong val)
>   {
> -    if (!riscv_feature(env, RISCV_FEATURE_MISA)) {
> +    if (!riscv_cpu_cfg(env)->misa_w) {
>           /* drop write to misa */
>           return RISCV_EXCP_NONE;
>       }

Re: [PATCH v7 03/10] target/riscv: allow MISA writes as experimental

[LIU Zhiwei]

On 2023/2/23 2:51, Daniel Henrique Barboza wrote:
> At this moment, and apparently since ever, we have no way of enabling
> RISCV_FEATURE_MISA. This means that all the code from write_misa(), all
> the nuts and bolts that handles how to properly write this CSR, has
> always been a no-op as well because write_misa() will always exit
> earlier.
>
> This seems to be benign in the majority of cases. Booting an Ubuntu
> 'virt' guest and logging all the calls to 'write_misa' shows that no
> writes to MISA CSR was attempted. Writing MISA, i.e. enabling/disabling
> RISC-V extensions after the machine is powered on, seems to be a niche
> use.
>
> After discussions in the mailing list, most notably in [1], we reached
> the consensus that this code is not suited to be exposed to users
> because it's not well tested, but at the same time removing it is a bit
> extreme because we would like to fix it, and it's easier to do so with
> the code available to use instead of fetching it from git log.
>
> The approach taken here is to get rid of RISCV_FEATURE_MISA altogether
> and use a new experimental flag called x-misa-w. The default value is
> false, meaning that we're keeping the existing behavior of doing nothing
> if a write_misa() is attempted. As with any existing experimental flag,
> x-misa-w is also a temporary flag that we need to remove once we fix
> write_misa().
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05092.html
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>   target/riscv/cpu.c | 6 ++++++
>   target/riscv/cpu.h | 2 +-
>   target/riscv/csr.c | 2 +-
>   3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 93b52b826c..1d637b1acd 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -1210,6 +1210,12 @@ static Property riscv_cpu_properties[] = {
>   
>       DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
>       DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
> +
> +    /*
> +     * write_misa() is marked as experimental for now so mark
> +     * it with -x and default to 'false'.
> +     */
> +    DEFINE_PROP_BOOL("x-misa-w", RISCVCPU, cfg.misa_w, false),
>       DEFINE_PROP_END_OF_LIST(),
>   };
>   
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 215423499e..9d3304bcda 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -89,7 +89,6 @@ enum {
>       RISCV_FEATURE_MMU,
>       RISCV_FEATURE_PMP,
>       RISCV_FEATURE_EPMP,
> -    RISCV_FEATURE_MISA,
>       RISCV_FEATURE_DEBUG
>   };
>   
> @@ -498,6 +497,7 @@ struct RISCVCPUConfig {
>       bool pmp;
>       bool epmp;
>       bool debug;
> +    bool misa_w;
>   
>       bool short_isa_string;
>   };
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index e149b453da..3cb8d2ffad 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -1329,7 +1329,7 @@ static RISCVException read_misa(CPURISCVState *env, int csrno,
>   static RISCVException write_misa(CPURISCVState *env, int csrno,
>                                    target_ulong val)
>   {
> -    if (!riscv_feature(env, RISCV_FEATURE_MISA)) {
> +    if (!riscv_cpu_cfg(env)->misa_w) {

Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>


Zhiwei

>           /* drop write to misa */
>           return RISCV_EXCP_NONE;
>       }

Re: [PATCH v7 00/10] make write_misa a no-op and FEATURE_* cleanups

[Palmer Dabbelt]

On Wed, 22 Feb 2023 10:51:55 PST (-0800), dbarboza@ventanamicro.com wrote:
> Hi,
>
> In this version we gave up removing all the write_misa() body and,
> instead, we went back to something closer to what we were doing in v2.
> write_misa() is now gated behind an experimental x-misa-w cfg option,
> defaulted to false.
>
> The idea is that x-misa-w allow us to keep experimenting and testing the
> code. Marking it as experimental will (hopefully) make users wary of the
> fact that this feature is unstable. The expectation is that the flag will
> be removed once write_misa() is ready to always write MISA.
>
> Changes from v6:
> - patches without reviews/acks: patch 3
> - patch 2: taken from version 3, acks and r-bs preserved
> - patch 3:
>   - rename 'misa-w' to 'x-misa-w' to be clearer about our intents with
>     the cfg option
> - v6 link: https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05047.html
>
> Daniel Henrique Barboza (10):
>   target/riscv: introduce riscv_cpu_cfg()
>   target/riscv: do not mask unsupported QEMU extensions in write_misa()
>   target/riscv: allow MISA writes as experimental
>   target/riscv: remove RISCV_FEATURE_DEBUG
>   target/riscv/cpu.c: error out if EPMP is enabled without PMP
>   target/riscv: remove RISCV_FEATURE_EPMP
>   target/riscv: remove RISCV_FEATURE_PMP
>   hw/riscv/virt.c: do not use RISCV_FEATURE_MMU in
>     create_fdt_socket_cpus()
>   target/riscv: remove RISCV_FEATURE_MMU
>   target/riscv/cpu: remove CPUArchState::features and friends
>
>  hw/riscv/virt.c           |  7 ++++---
>  target/riscv/cpu.c        | 25 ++++++++++---------------
>  target/riscv/cpu.h        | 29 ++++++-----------------------
>  target/riscv/cpu_helper.c |  6 +++---
>  target/riscv/csr.c        | 15 ++++++---------
>  target/riscv/machine.c    | 11 ++++-------
>  target/riscv/monitor.c    |  2 +-
>  target/riscv/op_helper.c  |  2 +-
>  target/riscv/pmp.c        |  8 ++++----
>  9 files changed, 39 insertions(+), 66 deletions(-)

I just queued this up, using the text from the v1 as that's more of a 
description of the patch set.  I think that text is still sufficiently 
accurate, but let me know if I missed anything.  Here's what I ended up 
with

    Merge patch series "make write_misa a no-op and FEATURE_* cleanups"
    
    Daniel Henrique Barboza <dbarboza@ventanamicro.com> says:
    
    The RISCV_FEATURES_* enum and the CPUArchState::features attribute were
    introduced 4+ years ago, as a way to retrieve the enabled hart features
    that aren't represented via MISA CSR bits. Time passed on, and
    RISCVCPUConfig was introduced. With it, we now have a centralized way of
    reading all hart features that are enabled/disabled by the user and the
    board. All recent features are reading their correspondent cpu->cfg.X
    flag.
    
    All but the 5 features in the RISCV_FEATURE_* enum. These features are
    still operating in the same way: set it during riscv_cpu_realize() using
    their cpu->cfg value, read it using riscv_feature() when needed. There
    is nothing special about them in comparison with all the other features
    and extensions to justify this special handling.
    
    This series then is doing two things: first we're actually allowing
    users to write the MISA CSR if they so choose. Then we're deprecate each
    RISC_FEATURE_* usage until, in patch 11, we remove everything related to
    it. All 5 existing RISCV_FEATURE_* features will be handled as everyone
    else.

Thanks!

Re: [PATCH v7 00/10] make write_misa a no-op and FEATURE_* cleanups

[Daniel Henrique Barboza]

On 3/1/23 20:43, Palmer Dabbelt wrote:
> On Wed, 22 Feb 2023 10:51:55 PST (-0800), dbarboza@ventanamicro.com wrote:
>> Hi,
>>
>> In this version we gave up removing all the write_misa() body and,
>> instead, we went back to something closer to what we were doing in v2.
>> write_misa() is now gated behind an experimental x-misa-w cfg option,
>> defaulted to false.
>>
>> The idea is that x-misa-w allow us to keep experimenting and testing the
>> code. Marking it as experimental will (hopefully) make users wary of the
>> fact that this feature is unstable. The expectation is that the flag will
>> be removed once write_misa() is ready to always write MISA.
>>
>> Changes from v6:
>> - patches without reviews/acks: patch 3
>> - patch 2: taken from version 3, acks and r-bs preserved
>> - patch 3:
>>   - rename 'misa-w' to 'x-misa-w' to be clearer about our intents with
>>     the cfg option
>> - v6 link: https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05047.html
>>
>> Daniel Henrique Barboza (10):
>>   target/riscv: introduce riscv_cpu_cfg()
>>   target/riscv: do not mask unsupported QEMU extensions in write_misa()
>>   target/riscv: allow MISA writes as experimental
>>   target/riscv: remove RISCV_FEATURE_DEBUG
>>   target/riscv/cpu.c: error out if EPMP is enabled without PMP
>>   target/riscv: remove RISCV_FEATURE_EPMP
>>   target/riscv: remove RISCV_FEATURE_PMP
>>   hw/riscv/virt.c: do not use RISCV_FEATURE_MMU in
>>     create_fdt_socket_cpus()
>>   target/riscv: remove RISCV_FEATURE_MMU
>>   target/riscv/cpu: remove CPUArchState::features and friends
>>
>>  hw/riscv/virt.c           |  7 ++++---
>>  target/riscv/cpu.c        | 25 ++++++++++---------------
>>  target/riscv/cpu.h        | 29 ++++++-----------------------
>>  target/riscv/cpu_helper.c |  6 +++---
>>  target/riscv/csr.c        | 15 ++++++---------
>>  target/riscv/machine.c    | 11 ++++-------
>>  target/riscv/monitor.c    |  2 +-
>>  target/riscv/op_helper.c  |  2 +-
>>  target/riscv/pmp.c        |  8 ++++----
>>  9 files changed, 39 insertions(+), 66 deletions(-)
> 
> I just queued this up, using the text from the v1 as that's more of a description of the patch set.  I think that text is still sufficiently accurate, but let me know if I missed anything.  Here's what I ended up with
> 
>     Merge patch series "make write_misa a no-op and FEATURE_* cleanups"
>     Daniel Henrique Barboza <dbarboza@ventanamicro.com> says:
>     The RISCV_FEATURES_* enum and the CPUArchState::features attribute were
>     introduced 4+ years ago, as a way to retrieve the enabled hart features
>     that aren't represented via MISA CSR bits. Time passed on, and
>     RISCVCPUConfig was introduced. With it, we now have a centralized way of
>     reading all hart features that are enabled/disabled by the user and the
>     board. All recent features are reading their correspondent cpu->cfg.X
>     flag.
>     All but the 5 features in the RISCV_FEATURE_* enum. These features are
>     still operating in the same way: set it during riscv_cpu_realize() using
>     their cpu->cfg value, read it using riscv_feature() when needed. There
>     is nothing special about them in comparison with all the other features
>     and extensions to justify this special handling.
>     This series then is doing two things: first we're actually allowing
>     users to write the MISA CSR if they so choose. Then we're deprecate each
>     RISC_FEATURE_* usage until, in patch 11, we remove everything related to
>     it. All 5 existing RISCV_FEATURE_* features will be handled as everyone
>     else.

LGTM!


Thanks,


Daniel

> 
> Thanks!

Re: [PATCH v7 03/10] target/riscv: allow MISA writes as experimental

[LIU Zhiwei]

On 2023/2/23 2:51, Daniel Henrique Barboza wrote:
> At this moment, and apparently since ever, we have no way of enabling
> RISCV_FEATURE_MISA. This means that all the code from write_misa(), all
> the nuts and bolts that handles how to properly write this CSR, has
> always been a no-op as well because write_misa() will always exit
> earlier.
>
> This seems to be benign in the majority of cases. Booting an Ubuntu
> 'virt' guest and logging all the calls to 'write_misa' shows that no
> writes to MISA CSR was attempted. Writing MISA, i.e. enabling/disabling
> RISC-V extensions after the machine is powered on, seems to be a niche
> use.
>
> After discussions in the mailing list, most notably in [1], we reached
> the consensus that this code is not suited to be exposed to users
> because it's not well tested, but at the same time removing it is a bit
> extreme because we would like to fix it, and it's easier to do so with
> the code available to use instead of fetching it from git log.
>
> The approach taken here is to get rid of RISCV_FEATURE_MISA altogether
> and use a new experimental flag called x-misa-w. The default value is
> false, meaning that we're keeping the existing behavior of doing nothing
> if a write_misa() is attempted. As with any existing experimental flag,
> x-misa-w is also a temporary flag that we need to remove once we fix
> write_misa().
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05092.html
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>   target/riscv/cpu.c | 6 ++++++
>   target/riscv/cpu.h | 2 +-
>   target/riscv/csr.c | 2 +-
>   3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 93b52b826c..1d637b1acd 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -1210,6 +1210,12 @@ static Property riscv_cpu_properties[] = {
>   
>       DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
>       DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
> +
> +    /*
> +     * write_misa() is marked as experimental for now so mark
> +     * it with -x and default to 'false'.
> +     */
> +    DEFINE_PROP_BOOL("x-misa-w", RISCVCPU, cfg.misa_w, false),

Just a question  I got when I reviewed another patch set:

Why put x-misa-w to riscv_cpu_properties instead of riscv_cpu_extensions?

I think this property should have a fixed value for a named cpu(such as 
sifive_e). Therefore IMHO, putting x-misa-w into riscv_cpu_extensions is 
more proper. At the same time,  the debug, rvv_ta_all_1s,  
rvv_ma_all_1s, resetvec properties should be moved to 
riscv_cpu_extentions. I am not sure why we should give the 
marchid/mipid/mvendorid option for named cpus. Maybe @Frank knows.

Have I missed something?

Zhiwei

>       DEFINE_PROP_END_OF_LIST(),
>   };
>   
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 215423499e..9d3304bcda 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -89,7 +89,6 @@ enum {
>       RISCV_FEATURE_MMU,
>       RISCV_FEATURE_PMP,
>       RISCV_FEATURE_EPMP,
> -    RISCV_FEATURE_MISA,
>       RISCV_FEATURE_DEBUG
>   };
>   
> @@ -498,6 +497,7 @@ struct RISCVCPUConfig {
>       bool pmp;
>       bool epmp;
>       bool debug;
> +    bool misa_w;
>   
>       bool short_isa_string;
>   };
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index e149b453da..3cb8d2ffad 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -1329,7 +1329,7 @@ static RISCVException read_misa(CPURISCVState *env, int csrno,
>   static RISCVException write_misa(CPURISCVState *env, int csrno,
>                                    target_ulong val)
>   {
> -    if (!riscv_feature(env, RISCV_FEATURE_MISA)) {
> +    if (!riscv_cpu_cfg(env)->misa_w) {
>           /* drop write to misa */
>           return RISCV_EXCP_NONE;
>       }

Re: [PATCH v7 03/10] target/riscv: allow MISA writes as experimental

[Daniel Henrique Barboza]

On 3/9/23 03:11, LIU Zhiwei wrote:
> 
> On 2023/2/23 2:51, Daniel Henrique Barboza wrote:
>> At this moment, and apparently since ever, we have no way of enabling
>> RISCV_FEATURE_MISA. This means that all the code from write_misa(), all
>> the nuts and bolts that handles how to properly write this CSR, has
>> always been a no-op as well because write_misa() will always exit
>> earlier.
>>
>> This seems to be benign in the majority of cases. Booting an Ubuntu
>> 'virt' guest and logging all the calls to 'write_misa' shows that no
>> writes to MISA CSR was attempted. Writing MISA, i.e. enabling/disabling
>> RISC-V extensions after the machine is powered on, seems to be a niche
>> use.
>>
>> After discussions in the mailing list, most notably in [1], we reached
>> the consensus that this code is not suited to be exposed to users
>> because it's not well tested, but at the same time removing it is a bit
>> extreme because we would like to fix it, and it's easier to do so with
>> the code available to use instead of fetching it from git log.
>>
>> The approach taken here is to get rid of RISCV_FEATURE_MISA altogether
>> and use a new experimental flag called x-misa-w. The default value is
>> false, meaning that we're keeping the existing behavior of doing nothing
>> if a write_misa() is attempted. As with any existing experimental flag,
>> x-misa-w is also a temporary flag that we need to remove once we fix
>> write_misa().
>>
>> [1] https://lists.gnu.org/archive/html/qemu-devel/2023-02/msg05092.html
>>
>> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>> ---
>>   target/riscv/cpu.c | 6 ++++++
>>   target/riscv/cpu.h | 2 +-
>>   target/riscv/csr.c | 2 +-
>>   3 files changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
>> index 93b52b826c..1d637b1acd 100644
>> --- a/target/riscv/cpu.c
>> +++ b/target/riscv/cpu.c
>> @@ -1210,6 +1210,12 @@ static Property riscv_cpu_properties[] = {
>>       DEFINE_PROP_BOOL("rvv_ta_all_1s", RISCVCPU, cfg.rvv_ta_all_1s, false),
>>       DEFINE_PROP_BOOL("rvv_ma_all_1s", RISCVCPU, cfg.rvv_ma_all_1s, false),
>> +
>> +    /*
>> +     * write_misa() is marked as experimental for now so mark
>> +     * it with -x and default to 'false'.
>> +     */
>> +    DEFINE_PROP_BOOL("x-misa-w", RISCVCPU, cfg.misa_w, false),
> 
> Just a question  I got when I reviewed another patch set:
> 
> Why put x-misa-w to riscv_cpu_properties instead of riscv_cpu_extensions?

I didn't think too much about it to be honest. I copied what was being done
with the now old RISCV_FEATURE_DEBUG. It made sense to me because x-misa-w
isn't a RISC-V extension but a property of our model.

I don't oppose moving it to a better place. Just be aware that this a property
that we're planning to eventually remove.


Thanks,


Daniel


> 
> I think this property should have a fixed value for a named cpu(such as sifive_e). Therefore IMHO, putting x-misa-w into riscv_cpu_extensions is more proper. At the same time,  the debug, rvv_ta_all_1s, rvv_ma_all_1s, resetvec properties should be moved to riscv_cpu_extentions. I am not sure why we should give the marchid/mipid/mvendorid option for named cpus. Maybe @Frank knows.
> 
> Have I missed something?
> 
> Zhiwei
> 
>>       DEFINE_PROP_END_OF_LIST(),
>>   };
>> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
>> index 215423499e..9d3304bcda 100644
>> --- a/target/riscv/cpu.h
>> +++ b/target/riscv/cpu.h
>> @@ -89,7 +89,6 @@ enum {
>>       RISCV_FEATURE_MMU,
>>       RISCV_FEATURE_PMP,
>>       RISCV_FEATURE_EPMP,
>> -    RISCV_FEATURE_MISA,
>>       RISCV_FEATURE_DEBUG
>>   };
>> @@ -498,6 +497,7 @@ struct RISCVCPUConfig {
>>       bool pmp;
>>       bool epmp;
>>       bool debug;
>> +    bool misa_w;
>>       bool short_isa_string;
>>   };
>> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
>> index e149b453da..3cb8d2ffad 100644
>> --- a/target/riscv/csr.c
>> +++ b/target/riscv/csr.c
>> @@ -1329,7 +1329,7 @@ static RISCVException read_misa(CPURISCVState *env, int csrno,
>>   static RISCVException write_misa(CPURISCVState *env, int csrno,
>>                                    target_ulong val)
>>   {
>> -    if (!riscv_feature(env, RISCV_FEATURE_MISA)) {
>> +    if (!riscv_cpu_cfg(env)->misa_w) {
>>           /* drop write to misa */
>>           return RISCV_EXCP_NONE;
>>       }