Re: [Qemu-devel] [PATCH] target-arm: Correct sense of the DCZID DZP bit

[Christopher Covington <cov@codeaurora.org>]

On 10/10/2014 12:49 PM, Peter Maydell wrote:
> The DZP bit in the DCZID system register should be set if
> the control bits which prohibit use of the DC ZVA instruction
> have been set (it stands for Data Zero Prohibited). However
> we had the sense of the test inverted; fix this so that the
> bit reads correctly.
> 
> To avoid this regressing the behaviour of the user-mode
> emulator, we must set the DZE bit in the SCTLR for that
> config so that userspace continues to see DZP as zero (it
> was getting the correct result by accident previously).
> 
> Reported-by: Christopher Covington <cov@codeaurora.org>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  target-arm/cpu.c    | 4 ++--
>  target-arm/helper.c | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/target-arm/cpu.c b/target-arm/cpu.c
> index edfd586..28e2701 100644
> --- a/target-arm/cpu.c
> +++ b/target-arm/cpu.c
> @@ -102,8 +102,8 @@ static void arm_cpu_reset(CPUState *s)
>          env->aarch64 = 1;
>  #if defined(CONFIG_USER_ONLY)
>          env->pstate = PSTATE_MODE_EL0t;
> -        /* Userspace expects access to CTL_EL0 and the cache ops */
> -        env->cp15.c1_sys |= SCTLR_UCT | SCTLR_UCI;
> +        /* Userspace expects access to DC ZVA, CTL_EL0 and the cache ops */
> +        env->cp15.c1_sys |= SCTLR_UCT | SCTLR_UCI | SCTLR_DZE;
>          /* and to the FP/Neon instructions */
>          env->cp15.c1_coproc = deposit64(env->cp15.c1_coproc, 20, 2, 3);
>  #else
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 2669e15..904f101 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -2018,7 +2018,7 @@ static uint64_t aa64_dczid_read(CPUARMState *env, const ARMCPRegInfo *ri)
>      int dzp_bit = 1 << 4;
>  
>      /* DZP indicates whether DC ZVA access is allowed */
> -    if (aa64_zva_access(env, NULL) != CP_ACCESS_OK) {
> +    if (aa64_zva_access(env, NULL) == CP_ACCESS_OK) {
>          dzp_bit = 0;
>      }
>      return cpu->dcz_blocksize | dzp_bit;
> 

Reviewed-by: Christopher Covington <cov@codeaurora.org>

Thanks Peter!

Christopher

-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project