Re: [PATCH] target/riscv: hardwire bits in hideleg and hedeleg

[LIU Zhiwei]

On 5/22/21 11:59 PM, Jose Martins wrote:

> The specification mandates for certain bits to be hardwired in the
> hypervisor delegation registers. This was not being enforced.
>
> Signed-off-by: Jose Martins <josemartins90@gmail.com>
> ---
>  target/riscv/csr.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index d2585395bf..9b74a00cc9 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -394,6 +394,7 @@ static int read_timeh(CPURISCVState *env, int csrno, target_ulong *val)
>  
>  static const target_ulong delegable_ints = S_MODE_INTERRUPTS |
>                                             VS_MODE_INTERRUPTS;
> +static const target_ulong vs_delegable_ints = VS_MODE_INTERRUPTS;
>     
    We can use it directly if only one macro VS_MODE_INTERRUPTS.
>  static const target_ulong all_ints = M_MODE_INTERRUPTS | S_MODE_INTERRUPTS |
>                                       VS_MODE_INTERRUPTS;
>  static const target_ulong delegable_excps =
> @@ -416,6 +417,14 @@ static const target_ulong delegable_excps =
>      (1ULL << (RISCV_EXCP_LOAD_GUEST_ACCESS_FAULT)) |
>      (1ULL << (RISCV_EXCP_VIRT_INSTRUCTION_FAULT)) |
>      (1ULL << (RISCV_EXCP_STORE_GUEST_AMO_ACCESS_FAULT));
> +static const target_ulong vs_delegable_excps = delegable_excps &
> +    ~((1ULL << (RISCV_EXCP_S_ECALL)) |
> +    (1ULL << (RISCV_EXCP_VS_ECALL)) |
>     
    I didn't find that the RISCV_EXCP_VS_ECALL should be read-only 0
    from the specification.
> +    (1ULL << (RISCV_EXCP_M_ECALL)) |
> +    (1ULL << (RISCV_EXCP_INST_GUEST_PAGE_FAULT)) |
> +    (1ULL << (RISCV_EXCP_LOAD_GUEST_ACCESS_FAULT)) |
> +    (1ULL << (RISCV_EXCP_VIRT_INSTRUCTION_FAULT)) |
> +    (1ULL << (RISCV_EXCP_STORE_GUEST_AMO_ACCESS_FAULT)));
>  static const target_ulong sstatus_v1_10_mask = SSTATUS_SIE | SSTATUS_SPIE |
>      SSTATUS_UIE | SSTATUS_UPIE | SSTATUS_SPP | SSTATUS_FS | SSTATUS_XS |
>      SSTATUS_SUM | SSTATUS_MXR | SSTATUS_SD;
> @@ -963,7 +972,7 @@ static int read_hedeleg(CPURISCVState *env, int csrno, target_ulong *val)
>  
>  static int write_hedeleg(CPURISCVState *env, int csrno, target_ulong val)
>  {
> -    env->hedeleg = val;
> +    env->hedeleg = val & vs_delegable_excps;
>

I think it's OK here.

However, as hedeleg is WARL, you had better reserve the other fields like medeleg:

	env->medeleg = (env->medeleg & ~delegable_excps) | (val & delegable_excps);

I really don't understand why medeleg codes this way. Is there anyone can give a better explanation?

>      return 0;
>  }
>  
> @@ -975,7 +984,7 @@ static int read_hideleg(CPURISCVState *env, int csrno, target_ulong *val)
>  
>  static int write_hideleg(CPURISCVState *env, int csrno, target_ulong val)
>  {
> -    env->hideleg = val;
> +    env->hideleg = val & vs_delegable_ints;
>      return 0;
>  }
>

The similar comments for hedeleg.

Zhiwei

>