Re: [Qemu-devel] [PATCH v2 1/6] target-arm: correct CNTFRQ access rights

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Thu, Feb 11, 2016 at 04:03:24PM +0000, Peter Maydell wrote:
> Correct some corner cases we were getting wrong for
> CNTFRQ access rights:
>  * should UNDEF from 32-bit Secure EL1
>  * only writable from the highest implemented exception level,
>    which might not be EL1 now
> 
> To clarify the code, provide a new utility function
> arm_highest_el() which returns the highest implemented
> exception level.

Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>


> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> Rewritten to use arm_highest_el() to improve clarity
> ---
>  target-arm/cpu.h    | 12 ++++++++++++
>  target-arm/helper.c | 29 ++++++++++++++++++++++++++---
>  2 files changed, 38 insertions(+), 3 deletions(-)
> 
> diff --git a/target-arm/cpu.h b/target-arm/cpu.h
> index 5137632..afbf366 100644
> --- a/target-arm/cpu.h
> +++ b/target-arm/cpu.h
> @@ -1255,6 +1255,18 @@ static inline bool cptype_valid(int cptype)
>  #define PL1_RW (PL1_R | PL1_W)
>  #define PL0_RW (PL0_R | PL0_W)
>  
> +/* Return the highest implemented Exception Level */
> +static inline int arm_highest_el(CPUARMState *env)
> +{
> +    if (arm_feature(env, ARM_FEATURE_EL3)) {
> +        return 3;
> +    }
> +    if (arm_feature(env, ARM_FEATURE_EL2)) {
> +        return 2;
> +    }
> +    return 1;
> +}
> +
>  /* Return the current Exception Level (as per ARMv8; note that this differs
>   * from the ARMv7 Privilege Level).
>   */
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 2f9db72..4d27c00 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -1218,10 +1218,33 @@ static const ARMCPRegInfo v6k_cp_reginfo[] = {
>  static CPAccessResult gt_cntfrq_access(CPUARMState *env, const ARMCPRegInfo *ri,
>                                         bool isread)
>  {
> -    /* CNTFRQ: not visible from PL0 if both PL0PCTEN and PL0VCTEN are zero */
> -    if (arm_current_el(env) == 0 && !extract32(env->cp15.c14_cntkctl, 0, 2)) {
> -        return CP_ACCESS_TRAP;
> +    /* CNTFRQ: not visible from PL0 if both PL0PCTEN and PL0VCTEN are zero.
> +     * Writable only at the highest implemented exception level.
> +     */
> +    int el = arm_current_el(env);
> +
> +    switch (el) {
> +    case 0:
> +        if (!extract32(env->cp15.c14_cntkctl, 0, 2)) {
> +            return CP_ACCESS_TRAP;
> +        }
> +        break;
> +    case 1:
> +        if (!isread && ri->state == ARM_CP_STATE_AA32 &&
> +            arm_is_secure_below_el3(env)) {
> +            /* Accesses from 32-bit Secure EL1 UNDEF (*not* trap to EL3!) */
> +            return CP_ACCESS_TRAP_UNCATEGORIZED;
> +        }
> +        break;
> +    case 2:
> +    case 3:
> +        break;
>      }
> +
> +    if (!isread && el < arm_highest_el(env)) {
> +        return CP_ACCESS_TRAP_UNCATEGORIZED;
> +    }
> +
>      return CP_ACCESS_OK;
>  }
>  
> -- 
> 1.9.1
>