Re: [PATCH v2 3/3] target-arm: Implement the S2 MMU inputsize > pamax check

["Alex Bennée" <alex.bennee@linaro.org>]

Edgar E. Iglesias <edgar.iglesias@gmail.com> writes:

> From: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>
>
> Implement the inputsize > pamax check for Stage 2 translations.
> We have multiple choices for how to respond to errors and
> choose to fault.
>
> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
> ---
>  target-arm/helper.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 4abeb4d..9a7ff5e 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -6808,7 +6808,7 @@ static bool get_phys_addr_lpae(CPUARMState *env, target_ulong address,
>           */
>          int startlevel = extract32(tcr->raw_tcr, 6, 2);
>          unsigned int pamax = arm_pamax(cpu);
> -        bool ok;
> +        bool ok = true;
>
>          if (va_size == 32 || stride == 9) {
>              /* AArch32 or 4KB pages */
> @@ -6818,9 +6818,17 @@ static bool get_phys_addr_lpae(CPUARMState *env, target_ulong address,
>              level = 3 - startlevel;
>          }
>
> -        /* Check that the starting level is valid. */
> -        ok = check_s2_startlevel(cpu, va_size == 64, level,
> -                                 inputsize, stride, pamax);
> +        if (va_size == 64 &&
> +            inputsize > pamax &&
> +            (arm_el_is_aa64(env, 1) || inputsize > 40)) {

If va_size == 64 doesn't that imply arm_el_is_aa64(env, 1)? Looking
further up the function it seems that is what sets va_size in the first
place. I think that makes the inputsize > 40 check redundant.

> +            /* We have multiple choices but choose to fault.  */
> +            ok = false;
> +        }
> +        if (ok) {
> +            /* Check that the starting level is valid. */
> +            ok = check_s2_startlevel(cpu, va_size == 64, level,
> +                                     inputsize, stride, pamax);
> +        }
>          if (!ok) {
>              /* AArch64 reports these as level 0 faults.
>               * AArch32 reports these as level 1 faults.

I'm not a fan of the ok = true / ok = false / ok =
check_s2_start_level() / if (!ok) ping-pong here as it is hard to
follow. I'm not sure how you could make it cleaner to follow though.
Maybe something like:

        /* For stage 2 translations the starting level is specified by the
         * VTCR_EL2.SL0 field (whose interpretation depends on the page size)
         */
        int startlevel = extract32(tcr->raw_tcr, 6, 2);
        unsigned int pamax = arm_pamax(cpu);
        bool is_aarch64_regime = (va_size == 64);
        bool ok;

        if (va_size == 32 || stride == 9) {
            /* AArch32 or 4KB pages */
            level = 2 - startlevel;
        } else {
            /* 16KB or 64KB pages */
            level = 3 - startlevel;
        }

        if (is_aarch64_regime &&
            inputsize > pamax) {
            /* We have multiple choices but choose to fault.  */
            ok = false;
        } else {
            /* Check that the starting level is valid. */
            ok = check_s2_startlevel(cpu, is_aarch64_regime, level,
                                     inputsize, stride, pamax);
        }
        if (!ok) {
            /* AArch64 reports these as level 0 faults.
             * AArch32 reports these as level 1 faults.
             */
            level = is_aarch64_regime ? 0 : 1;
            fault_type = translation_fault;
            goto do_fault;
        }

But I'm wondering if it just makes more sense to push the:

    is_aarch64_regime && inputsize > pamax

Check into check_s2_startlevel? Then you could just have a simple call
which succeeds or falls through to a fault?

        /* Check that the starting level is valid. */
        if (!check_s2_startlevel(cpu, is_aarch64_regime, level,
                                     inputsize, stride, pamax) ){
            /* AArch64 reports these as level 0 faults.
             * AArch32 reports these as level 1 faults.
             */
            level = is_aarch64_regime ? 0 : 1;
            fault_type = translation_fault;
            goto do_fault;
        }

--
Alex Bennée