Chapter 5 describes the CTR behavior when Smstaten is enabled, but it
does not talk about the CTR behavior when Smstateen is disabled, that
is, there is no mstateen0 and hstateen0 CSR.
The spec states:
* Attempts to access sctrdepth from VS-mode or VU-mode raise a
virtual-instruction exception, unless CTR state enable access
restrictions apply.
* sctrdepth is not included in the above list of supervisor CTR state
controlled by hstateen0.CTR since accesses to sctrdepth from VS-mode
raise a virtual-instruction exception regardless of the value of
hstateen0.CTR.
Below is my understanding:
* If Smstateen is enabled:
o If mstateen0.CTR=0:
+ Attempts to access sctrctl, vsctrctl, sctrdepth, or
sctrstatus raise an illegal-instruction exception for
privilege modes less privileged than M-mode.
+ Attempts to access sireg* when siselect is in 0x200..0x2FF,
or vsireg* when vsiselect is in 0x200..0x2FF raise an
illegal-instruction exception for privilege modes less
privileged than M-mode.
+ Execution of the SCTRCLR instruction raises an
illegal-instruction exception for privilege modes less
privileged than M-mode.
o If mstateen.CTR=1:
+ Attempts to access sctrctl, vsctrctl, sctrdepth, or
sctrstatus raise an illegal-instruction exception for U-mode.
+ Attempts to access sireg* when siselect is in 0x200..0x2FF,
or vsireg* when vsiselect is in 0x200..0x2FF raise an
illegal-instruction exception for U-mode.
+ Execution of the SCTRCLR instruction raises an
illegal-instruction exception for U-mode.
+ If H extension is enabled:
# If hstateen0.CTR = 0:
* Attempts to access sctrctl, vsctrctl, sctrdepth, or
sctrstatus raise an virtual-instruction exception
for VU-mode and VS-mode.
* Attempts to access sireg* when siselect is in
0x200..0x2FF, or vsireg* when vsiselect is in
0x200..0x2FF raise an virtual-instruction exception
for VU-mode and VS-mode.
* Execution of the SCTRCLR instruction raises an
virtual-instruction exception for VU-mode and VS-mode.
# If hstateen0.CTR = 1:
* Attempts to access sctrctl, vsctrctl, sctrdepth, or
sctrstatus raise an virtual-instruction exception
for VU-mode.
* *_/Attempts to access sctrdepth raise an
virtual-instruction exception for "VS-mode"/._*
* Attempts to access sireg* when siselect is in
0x200..0x2FF, or vsireg* when vsiselect is in
0x200..0x2FF raise an virtual-instruction exception
for VU-mode.
* Execution of the SCTRCLR instruction raises an
virtual-instruction exception for VU-mode.
* If Smstateen is disabled:
o Attempts to access sctrctl, vsctrctl, sctrdepth, or sctrstatus
raise an illegal-instruction exception for U-mode.
o Attempts to access sireg* when siselect is in 0x200..0x2FF, or
vsireg* when vsiselect is in 0x200..0x2FF raise an
illegal-instruction exception for U-mode.
o Execution of the SCTRCLR instruction raises an
illegal-instruction exception for U-mode.
o If H extension is enabled:
+ Attempts to access sctrctl, vsctrctl, sctrdepth, or
sctrstatus raise an virtual-instruction exception for VU-mode.
+ */_Attempts to access sctrdepth raise an virtual-instruction
exception for "VS-mode"._/*
+ Attempts to access sireg* when siselect is in 0x200..0x2FF,
or vsireg* when vsiselect is in 0x200..0x2FF raise an
virtual-instruction exception for VU-mode.
+ Execution of the SCTRCLR instruction raises an
virtual-instruction exception for VU-mode.
If there is any misunderstanding, please let me know. Also Sstateen0
does not involve in CTR. Am I correct?
Thanks in advance.
Beeman Strong 於 2024/6/5 上午 02:46 寫道:
On Tue, Jun 4, 2024 at 10:19 AM Jason Chien <jason.ch...@sifive.com>
wrote:
Rajnesh Kanwal 於 2024/5/30 上午 12:09 寫道:
> CTR extension adds a new instruction sctrclr to quickly
> clear the recorded entries buffer.
>
> Signed-off-by: Rajnesh Kanwal <rkan...@rivosinc.com>
> ---
> target/riscv/cpu.h | 1 +
> target/riscv/cpu_helper.c | 7 +++++++
> target/riscv/insn32.decode | 1 +
> target/riscv/insn_trans/trans_privileged.c.inc | 10 ++++++++++
> target/riscv/op_helper.c | 5 +++++
> 5 files changed, 24 insertions(+)
>
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index a294a5372a..fade71aa09 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -572,6 +572,7 @@ void riscv_cpu_set_mode(CPURISCVState *env,
target_ulong newpriv, bool virt_en);
> void riscv_ctr_freeze(CPURISCVState *env, uint64_t freeze_mask);
> void riscv_ctr_add_entry(CPURISCVState *env, target_long src,
target_long dst,
> uint64_t type, target_ulong
prev_priv, bool prev_virt);
> +void riscv_ctr_clear(CPURISCVState *env);
>
> void riscv_translate_init(void);
> G_NORETURN void riscv_raise_exception(CPURISCVState *env,
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index e064a7306e..45502f50a7 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -704,6 +704,13 @@ void riscv_ctr_freeze(CPURISCVState *env,
uint64_t freeze_mask)
> }
> }
>
> +void riscv_ctr_clear(CPURISCVState *env)
> +{
> + memset(env->ctr_src, 0x0, sizeof(env->ctr_src));
> + memset(env->ctr_dst, 0x0, sizeof(env->ctr_dst));
> + memset(env->ctr_data, 0x0, sizeof(env->ctr_data));
> +}
> +
> static uint64_t riscv_ctr_priv_to_mask(target_ulong priv, bool
virt)
> {
> switch (priv) {
> diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
> index 9cb1a1b4ec..d3d38c7c68 100644
> --- a/target/riscv/insn32.decode
> +++ b/target/riscv/insn32.decode
> @@ -107,6 +107,7 @@
> # *** Privileged Instructions ***
> ecall 000000000000 00000 000 00000 1110011
> ebreak 000000000001 00000 000 00000 1110011
> +sctrclr 000100000100 00000 000 00000 1110011
> uret 0000000 00010 00000 000 00000 1110011
> sret 0001000 00010 00000 000 00000 1110011
> mret 0011000 00010 00000 000 00000 1110011
> diff --git a/target/riscv/insn_trans/trans_privileged.c.inc
b/target/riscv/insn_trans/trans_privileged.c.inc
> index 339d659151..dd9da8651f 100644
> --- a/target/riscv/insn_trans/trans_privileged.c.inc
> +++ b/target/riscv/insn_trans/trans_privileged.c.inc
> @@ -69,6 +69,16 @@ static bool trans_ebreak(DisasContext *ctx,
arg_ebreak *a)
> return true;
> }
>
> +static bool trans_sctrclr(DisasContext *ctx, arg_sctrclr *a)
> +{
> +#ifndef CONFIG_USER_ONLY
If both of smctr and ssctr are not enabled, it is an illegal
instruction.
> + gen_helper_ctr_clear(tcg_env);
> + return true;
> +#else
> + return false;
> +#endif
> +}
> +
> static bool trans_uret(DisasContext *ctx, arg_uret *a)
> {
> return false;
> diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
> index c8053d9c2f..89423c04b3 100644
> --- a/target/riscv/op_helper.c
> +++ b/target/riscv/op_helper.c
> @@ -461,6 +461,11 @@ void helper_ctr_branch(CPURISCVState *env,
target_ulong src, target_ulong dest,
> }
> }
>
> +void helper_ctr_clear(CPURISCVState *env)
> +{
There should be some checks here.
The spec states:
SCTRCLR raises an illegal-instruction exception in U-mode, and a
virtual-instruction exception in VU-mode, unless CTR state enable
access
restrictions apply.
I don't quite understand "unless CTR state enable access restrictions
apply" though.
The next sentence says "See Chapter 5", which states that execution of
SCTRCLR raises an illegal instruction exception if mstateen0.CTR=0 and
the priv mode is not M-mode, and it raises a virtual instruction
exception if mstateen0.CTR=0 && hstateen0.CTR=1 and the priv mode is
VS-mode.
When mstateen0.CTR=0, hstateen0.CTR is read-only 0. I guess you meant
"mstateen0.CTR=1 && hstateen0.CTR=0" here.
> + riscv_ctr_clear(env);
> +}
> +
> void helper_wfi(CPURISCVState *env)
> {
> CPUState *cs = env_cpu(env);
