Re: [PATCH 1/2] target/riscv: FIX xATP_MODE validation

[LIU Zhiwei]

Hi Irina,

On 2023/12/1 19:53, Irina Ryapolova wrote:
> The SATP register is an SXLEN-bit read/write WARL register. It means that CSR 
> fields are only defined
> for a subset of bit encodings, but allow any value to be written while 
> guaranteeing to return a legal
> value whenever read (See riscv-privileged-20211203, SATP CSR).
>
> For example on rv64 we are trying to write to SATP CSR val = 0x1000000000000000 
> (SATP_MODE = 1 - Reserved for standard use)
> and after that we are trying to read SATP_CSR. We read from the SATP CSR value 
> = 0x1000000000000000, which is not a correct
> operation (return illegal value).
>
> Signed-off-by: Irina Ryapolova <irina.ryapolova@syntacore.com>
> ---
>   target/riscv/csr.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index fde7ce1a53..6f244815b7 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -1278,8 +1278,8 @@ static RISCVException read_mstatus(CPURISCVState *env, 
> int csrno,
>   
>   static bool validate_vm(CPURISCVState *env, target_ulong vm)
>   {
> -    return (vm & 0xf) <=
> -           satp_mode_max_from_map(riscv_cpu_cfg(env)->satp_mode.map);
> +    uint64_t mode_supported = riscv_cpu_cfg(env)->satp_mode.supported;

Why not use satp_mode.map? Using satp_mode.supported will violate the 
SATP settings in cpu init.

Zhiwei

> +    return get_field(mode_supported, (1 << vm));
>   }
>   
>   static target_ulong legalize_mpp(CPURISCVState *env, target_ulong old_mpp,