Re: [RFC PATCH v5 2/4] target/riscv: smstateen check for h/senvcfg

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Re: [RFC PATCH v5 2/4] target/riscv: smstateen check for h/senvcfg

From:	Weiwei Li
Subject:	Re: [RFC PATCH v5 2/4] target/riscv: smstateen check for h/senvcfg
Date:	Fri, 8 Jul 2022 07:36:08 +0800
User-agent:	Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0

在 2022/7/8 上午1:20, Mayuresh Chitale 写道:

On Sat, 2022-07-02 at 18:33 +0800, angell1518 wrote:

At 2022-06-04 00:04:23, "Mayuresh Chitale" <mchitale@ventanamicro.com

wrote:
Accesses to henvcfg, henvcfgh and senvcfg are allowed
only if corresponding bit in mstateen0/hstateen0 is
enabled. Otherwise an illegal instruction trap is
generated.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
---
target/riscv/csr.c | 84 ++++++++++++++++++++++++++++++++++++++++++-

---

1 file changed, 78 insertions(+), 6 deletions(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 324fefce59..ae91ae1f7e 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.ccounteren
@@ -39,6 +39,37 @@ void riscv_set_csr_ops(int csrno,

riscv_csr_operations *ops)

}

/* Predicates */
+static RISCVException smstateen_acc_ok(CPURISCVState *env, int

mode, int bit)

+{
+    CPUState *cs = env_cpu(env);
+    RISCVCPU *cpu = RISCV_CPU(cs);
+    bool virt = riscv_cpu_virt_enabled(env);
+
+    if (!cpu->cfg.ext_smstateen) {
+        return RISCV_EXCP_NONE;
+    }
+
+#if !defined(CONFIG_USER_ONLY)
+    if (!(env->mstateen[0] & 1UL << bit)) {
+        return RISCV_EXCP_ILLEGAL_INST;
+    }
+

I think mstateen only control access in priv mode under M mode.  
So we should take the current priv node into consideration here.

For any curent priv mode if the required bit is not set in mstateen we
can return here itself. For e.g if current priv mode is S then we only
check the required bit in mstateen. If current priv mode is 'U', we
need to check the required bit in mstateen and sstateen

mstateen only controls the access from less-privilege mode. So do hstateen and sstateen.  we should pass all of the
check, if current priv is PRV_M. like this:
+    if (env->priv == PRV_M) {
+        return RISCV_EXCP_NONE;
+    }

+    if (virt) {
+        if (!(env->hstateen[0] & 1UL << bit)) {
+            return RISCV_EXCP_VIRT_INSTRUCTION_FAULT;
+        }
+    }
+
+    if (mode == PRV_U) {
+        if (!(env->sstateen[0] & 1UL << bit)) {
+            return RISCV_EXCP_ILLEGAL_INST;
+ }

I think there are two problem here:
The first is that we should also take virt mode into consideration
here too.

Actually virt mode is considered above for both priv modes S and U.

Yeah(we also should pass this check for current priv is PRV_M). However, there's still a problem

here: the mode here is the mode for csr not the current priv mode. Actually, Sstateen will control the access

for user mode csr(such as fcsr) from U mode. So taking the following question into consideration, the total check

may be:

+    if (mode == PRV_U && env->priv == PRV_U) {
+        if (riscv_has_ext(env, RVS) && !(env->sstateen[0] & 1UL << bit)) {
+            return RISCV_EXCP_ILLEGAL_INST;
+ }

Regards,
Weiwei Li

As the spec said: 
"if executing in VS or VU mode and the circumstances for a virtual
instruction
exception apply, raises a virtual instruction exception instead of an
illegal instruction exception"
So it will generate RISCV_EXCP_VIRT_INSTRUCTION_FAULT in VU mode.

The second is that sstateen csr works only when 'S' extension is
enabled

I will fix it in the next version.

Regards,
Weiwei Li

+    }
+#endif
+
+    return RISCV_EXCP_NONE;
+}
+
static RISCVException fs(CPURISCVState *env, int csrno)
{
#if !defined(CONFIG_USER_ONLY)
@@ -1557,6 +1588,13 @@ static RISCVException

write_menvcfgh(CPURISCVState *env, int csrno,

static RISCVException read_senvcfg(CPURISCVState *env, int csrno,
                                 target_ulong *val)
{
+    RISCVException ret;
+
+    ret = smstateen_acc_ok(env, PRV_S, SMSTATEEN0_HSENVCFG);
+    if (ret != RISCV_EXCP_NONE) {
+        return ret;
+    }
+
    *val = env->senvcfg;
    return RISCV_EXCP_NONE;
}
@@ -1565,15 +1603,27 @@ static RISCVException

write_senvcfg(CPURISCVState *env, int csrno,

                                  target_ulong val)
{
    uint64_t mask = SENVCFG_FIOM | SENVCFG_CBIE | SENVCFG_CBCFE |

SENVCFG_CBZE;

+    RISCVException ret;

-    env->senvcfg = (env->senvcfg & ~mask) | (val & mask);
+    ret = smstateen_acc_ok(env, PRV_S, SMSTATEEN0_HSENVCFG);
+    if (ret != RISCV_EXCP_NONE) {
+        return ret;
+    }

+    env->senvcfg = (env->senvcfg & ~mask) | (val & mask);
    return RISCV_EXCP_NONE;
}

static RISCVException read_henvcfg(CPURISCVState *env, int csrno,
                                 target_ulong *val)
{
+    RISCVException ret;
+
+    ret = smstateen_acc_ok(env, PRV_S, SMSTATEEN0_HSENVCFG);
+    if (ret != RISCV_EXCP_NONE) {
+        return ret;
+    }
+
    *val = env->henvcfg;
    return RISCV_EXCP_NONE;
}
@@ -1582,6 +1632,12 @@ static RISCVException

write_henvcfg(CPURISCVState *env, int csrno,

                                  target_ulong val)
{
    uint64_t mask = HENVCFG_FIOM | HENVCFG_CBIE | HENVCFG_CBCFE |

HENVCFG_CBZE;

+    RISCVException ret;
+
+    ret = smstateen_acc_ok(env, PRV_S, SMSTATEEN0_HSENVCFG);
+    if (ret != RISCV_EXCP_NONE) {
+        return ret;
+    }

    if (riscv_cpu_mxl(env) == MXL_RV64) {
        mask |= HENVCFG_PBMTE | HENVCFG_STCE;
@@ -1595,6 +1651,13 @@ static RISCVException

write_henvcfg(CPURISCVState *env, int csrno,

static RISCVException read_henvcfgh(CPURISCVState *env, int csrno,
                                 target_ulong *val)
{
+    RISCVException ret;
+
+    ret = smstateen_acc_ok(env, PRV_S, SMSTATEEN0_HSENVCFG);
+    if (ret != RISCV_EXCP_NONE) {
+        return ret;
+    }
+
    *val = env->henvcfg >> 32;
    return RISCV_EXCP_NONE;
}
@@ -1604,9 +1667,14 @@ static RISCVException

write_henvcfgh(CPURISCVState *env, int csrno,

{
    uint64_t mask = HENVCFG_PBMTE | HENVCFG_STCE;
    uint64_t valh = (uint64_t)val << 32;
+    RISCVException ret;

-    env->henvcfg = (env->henvcfg & ~mask) | (valh & mask);
+    ret = smstateen_acc_ok(env, PRV_S, SMSTATEEN0_HSENVCFG);
+    if (ret != RISCV_EXCP_NONE) {
+        return ret;
+    }

+    env->henvcfg = (env->henvcfg & ~mask) | (valh & mask);
    return RISCV_EXCP_NONE;
}

@@ -1628,7 +1696,8 @@ static RISCVException

write_mstateen(CPURISCVState *env, int csrno,

                                     target_ulong new_val)
{
    uint64_t *reg;
-    uint64_t wr_mask = 1UL << SMSTATEEN_STATEN;
+    uint64_t wr_mask = (1UL << SMSTATEEN_STATEN) |
+                       (1UL << SMSTATEEN0_HSENVCFG);

    reg = &env->mstateen[csrno - CSR_MSTATEEN0];
    write_smstateen(env, reg, wr_mask, new_val);
@@ -1649,7 +1718,8 @@ static RISCVException

write_mstateenh(CPURISCVState *env, int csrno,

{
    uint64_t *reg;
    uint64_t val;
-    uint64_t wr_mask = 1UL << SMSTATEEN_STATEN;
+    uint64_t wr_mask = (1UL << SMSTATEEN_STATEN) |
+                       (1UL << SMSTATEEN0_HSENVCFG);

    reg = &env->mstateen[csrno - CSR_MSTATEEN0H];
    val = (uint64_t)new_val << 32;
@@ -1671,7 +1741,8 @@ static RISCVException

write_hstateen(CPURISCVState *env, int csrno,

                                     target_ulong new_val)
{
    uint64_t *reg;
-    uint64_t wr_mask = 1UL << SMSTATEEN_STATEN;
+    uint64_t wr_mask = (1UL << SMSTATEEN_STATEN) |
+                       (1UL << SMSTATEEN0_HSENVCFG);
    int index = csrno - CSR_HSTATEEN0;

    reg = &env->hstateen[index];
@@ -1694,8 +1765,9 @@ static RISCVException

write_hstateenh(CPURISCVState *env, int csrno,

{
    uint64_t *reg;
    uint64_t val;
-    uint64_t wr_mask = 1UL << SMSTATEEN_STATEN;
    int index = csrno - CSR_HSTATEEN0H;
+    uint64_t wr_mask = (1UL << SMSTATEEN_STATEN) |
+                       (1UL << SMSTATEEN0_HSENVCFG);

    reg = &env->hstateen[index];
    val = (uint64_t)new_val << 32;
-- 
2.25.1

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Re:[RFC PATCH v5 2/4] target/riscv: smstateen check for h/senvcfg, angell1518, 2022/07/02
- Re: [RFC PATCH v5 2/4] target/riscv: smstateen check for h/senvcfg, Mayuresh Chitale, 2022/07/07
  - Re: [RFC PATCH v5 2/4] target/riscv: smstateen check for h/senvcfg, Weiwei Li <=

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