Re: [PATCH v6 4/4] target/riscv: Change the TLB page size depends on PMP entries.

[Alistair Francis]

On Tue, Jul 28, 2020 at 1:29 AM Zong Li <zong.li@sifive.com> wrote:
>
> The minimum granularity of PMP is 4 bytes, it is small than 4KB page
> size, therefore, the pmp checking would be ignored if its range doesn't
> start from the alignment of one page. This patch detects the pmp entries
> and sets the small page size to TLB if there is a PMP entry which cover
> the page size.
>
> Signed-off-by: Zong Li <zong.li@sifive.com>
> ---
>  target/riscv/cpu_helper.c | 10 ++++++--
>  target/riscv/pmp.c        | 52 +++++++++++++++++++++++++++++++++++++++
>  target/riscv/pmp.h        |  2 ++
>  3 files changed, 62 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 2f337e418c..fd1d373b6f 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -693,6 +693,7 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int 
> size,
>      bool first_stage_error = true;
>      int ret = TRANSLATE_FAIL;
>      int mode = mmu_idx;
> +    target_ulong tlb_size = 0;
>
>      env->guest_phys_fault_addr = 0;
>
> @@ -784,8 +785,13 @@ bool riscv_cpu_tlb_fill(CPUState *cs, vaddr address, int 
> size,
>      }
>
>      if (ret == TRANSLATE_SUCCESS) {
> -        tlb_set_page(cs, address & TARGET_PAGE_MASK, pa & TARGET_PAGE_MASK,
> -                     prot, mmu_idx, TARGET_PAGE_SIZE);
> +        if (pmp_is_range_in_tlb(env, pa & TARGET_PAGE_MASK, &tlb_size)) {
> +            tlb_set_page(cs, address & ~(tlb_size - 1), pa & ~(tlb_size - 1),
> +                         prot, mmu_idx, tlb_size);
> +        } else {
> +            tlb_set_page(cs, address & TARGET_PAGE_MASK, pa & 
> TARGET_PAGE_MASK,
> +                         prot, mmu_idx, TARGET_PAGE_SIZE);
> +        }
>          return true;
>      } else if (probe) {
>          return false;
> diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
> index aeba796484..adadf6e9ba 100644
> --- a/target/riscv/pmp.c
> +++ b/target/riscv/pmp.c
> @@ -393,3 +393,55 @@ target_ulong pmpaddr_csr_read(CPURISCVState *env, 
> uint32_t addr_index)
>
>      return val;
>  }
> +
> +/*
> + * Calculate the TLB size if the start address or the end address of
> + * PMP entry is presented in thie TLB page.
> + */
> +static target_ulong pmp_get_tlb_size(CPURISCVState *env, int pmp_index,
> +    target_ulong tlb_sa, target_ulong tlb_ea)
> +{
> +    target_ulong pmp_sa = env->pmp_state.addr[pmp_index].sa;
> +    target_ulong pmp_ea = env->pmp_state.addr[pmp_index].ea;
> +
> +    if (pmp_sa >= tlb_sa && pmp_ea <= tlb_ea) {
> +        return pmp_ea - pmp_sa + 1;
> +    }
> +
> +    if (pmp_sa >= tlb_sa && pmp_sa <= tlb_ea && pmp_ea >= tlb_ea) {
> +        return tlb_ea - pmp_sa + 1;
> +    }
> +
> +    if (pmp_ea <= tlb_ea && pmp_ea >= tlb_sa && pmp_sa <= tlb_sa) {
> +        return pmp_ea - tlb_sa + 1;
> +    }
> +
> +    return 0;
> +}
> +
> +/*
> + * Check is there a PMP entry whcih range covers this page. If so,

s/whcih/which/g

I fixed this when apply it.

> + * try to find the minimum granularity for the TLB size.
> + */
> +bool pmp_is_range_in_tlb(CPURISCVState *env, hwaddr tlb_sa,
> +    target_ulong *tlb_size)
> +{
> +    int i;
> +    target_ulong val;
> +    target_ulong tlb_ea = (tlb_sa + TARGET_PAGE_SIZE - 1);
> +
> +    for (i = 0; i < MAX_RISCV_PMPS; i++) {
> +        val = pmp_get_tlb_size(env, i, tlb_sa, tlb_ea);
> +        if (val) {
> +            if (*tlb_size == 0 || *tlb_size > val) {
> +                *tlb_size = val;
> +            }
> +        }
> +    }
> +
> +    if (*tlb_size != 0) {
> +        return true;
> +    }
> +
> +    return false;
> +}
> diff --git a/target/riscv/pmp.h b/target/riscv/pmp.h
> index 8e19793132..c70f2ea4c4 100644
> --- a/target/riscv/pmp.h
> +++ b/target/riscv/pmp.h
> @@ -60,5 +60,7 @@ void pmpaddr_csr_write(CPURISCVState *env, uint32_t 
> addr_index,
>  target_ulong pmpaddr_csr_read(CPURISCVState *env, uint32_t addr_index);
>  bool pmp_hart_has_privs(CPURISCVState *env, target_ulong addr,
>      target_ulong size, pmp_priv_t priv, target_ulong mode);
> +bool pmp_is_range_in_tlb(CPURISCVState *env, hwaddr tlb_sa,
> +    target_ulong *tlb_size);

The indentation is wrong here (as it is in the rest of the file). I
just fixed this up as well as the others when I applied it.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

I have applied patch 3 and 4 of this series. Patch 1 has already been
applied and patch 2 no longer applies due to a different fix, sorry
about that.

Alistair

>
>  #endif
> --
> 2.27.0
>
>