Re: [PATCH v3 12/12] target/riscv: Simplify probing in vext_ldff

[Max Chou]

Reviewed-by: Max Chou <max.chou@sifive.com>

On 2024/7/19 9:07 AM, Richard Henderson 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.
>
> Acked-by: Alistair Francis <alistair.francis@wdc.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   target/riscv/vector_helper.c | 31 +++++++++++++++++--------------
>   1 file changed, 17 insertions(+), 14 deletions(-)
>
> diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
> index 1b4d5a8e37..10a52ceb5b 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);
> +
> +                /*
> +                 * Stop if invalid (unmapped) or mmio (transaction may fail).
> +                 * Do not stop if watchpoint, as the spec says that
> +                 * first-fault should continue to access the same
> +                 * elements regardless of any watchpoint.
> +                 */
> +                if (flags & ~TLB_WATCHPOINT) {
>                       vl = i;
>                       goto ProbeSuccess;
>                   }
> -                if (remain <=  offset) {
> +                if (remain <= offset) {
>                       break;
>                   }
>                   remain -= offset;