Re: [PATCH v2 13/13] target/riscv: Simplify probing in vext_ldff

[Alistair Francis]

On Wed, Jul 10, 2024 at 1:30 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> The current pairing of tlb_vaddr_to_host with extra is either
> inefficient (user-only, with page_check_range) or incorrect
> (system, with probe_pages).
>
> For proper non-fault behaviour, use probe_access_flags with
> its nonfault parameter set to true.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

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

Alistair

> ---
>  target/riscv/vector_helper.c | 34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
>
> diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
> index 1b4d5a8e37..4d72eb74d3 100644
> --- a/target/riscv/vector_helper.c
> +++ b/target/riscv/vector_helper.c
> @@ -474,7 +474,6 @@ vext_ldff(void *vd, void *v0, target_ulong base,
>            vext_ldst_elem_fn *ldst_elem,
>            uint32_t log2_esz, uintptr_t ra)
>  {
> -    void *host;
>      uint32_t i, k, vl = 0;
>      uint32_t nf = vext_nf(desc);
>      uint32_t vm = vext_vm(desc);
> @@ -493,27 +492,31 @@ vext_ldff(void *vd, void *v0, target_ulong base,
>          }
>          addr = adjust_addr(env, base + i * (nf << log2_esz));
>          if (i == 0) {
> +            /* Allow fault on first element. */
>              probe_pages(env, addr, nf << log2_esz, ra, MMU_DATA_LOAD);
>          } else {
> -            /* if it triggers an exception, no need to check watchpoint */
>              remain = nf << log2_esz;
>              while (remain > 0) {
> +                void *host;
> +                int flags;
> +
>                  offset = -(addr | TARGET_PAGE_MASK);
> -                host = tlb_vaddr_to_host(env, addr, MMU_DATA_LOAD, 
> mmu_index);
> -                if (host) {
> -#ifdef CONFIG_USER_ONLY
> -                    if (!page_check_range(addr, offset, PAGE_READ)) {
> -                        vl = i;
> -                        goto ProbeSuccess;
> -                    }
> -#else
> -                    probe_pages(env, addr, offset, ra, MMU_DATA_LOAD);
> -#endif
> -                } else {
> +
> +                /* Probe nonfault on subsequent elements. */
> +                flags = probe_access_flags(env, addr, offset, MMU_DATA_LOAD,
> +                                           mmu_index, true, &host, 0);
> +                if (flags) {
> +                    /*
> +                     * Stop any flag bit set:
> +                     *   invalid (unmapped)
> +                     *   mmio (transaction failed)
> +                     *   watchpoint (debug)
> +                     * In all cases, handle as the first load next time.
> +                     */
>                      vl = i;
> -                    goto ProbeSuccess;
> +                    break;
>                  }
> -                if (remain <=  offset) {
> +                if (remain <= offset) {
>                      break;
>                  }
>                  remain -= offset;
> @@ -521,7 +524,6 @@ vext_ldff(void *vd, void *v0, target_ulong base,
>              }
>          }
>      }
> -ProbeSuccess:
>      /* load bytes from guest memory */
>      if (vl != 0) {
>          env->vl = vl;
> --
> 2.43.0
>
>