Re: [PATCH 3/3] target/arm: Handle trapping to EL2 of AArch32 VMRS instructions

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

On Thu, Nov 28, 2019 at 04:17:18PM +0000, Marc Zyngier wrote:
> HCR_EL2.TID3 requires that AArch32 reads of MVFR[012] are trapped to
> EL2, and that HCR_EL2.TID0 does the same for reads of FPSID.
> In order to handle this, introduce a new TCG helper function that
> checks for these control bits before executing the VMRC instruction.
> 
> Tested with a hacked-up version of KVM/arm64 that sets the control
> bits for 32bit guests.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  target/arm/helper-a64.h        |  2 ++
>  target/arm/internals.h         |  8 ++++++++
>  target/arm/translate-vfp.inc.c | 12 +++++++++---
>  target/arm/vfp_helper.c        | 27 +++++++++++++++++++++++++++
>  4 files changed, 46 insertions(+), 3 deletions(-)
> 
> diff --git a/target/arm/helper-a64.h b/target/arm/helper-a64.h
> index a915c1247f..311ced44e6 100644
> --- a/target/arm/helper-a64.h
> +++ b/target/arm/helper-a64.h
> @@ -102,3 +102,5 @@ DEF_HELPER_FLAGS_3(autda, TCG_CALL_NO_WG, i64, env, i64, i64)
>  DEF_HELPER_FLAGS_3(autdb, TCG_CALL_NO_WG, i64, env, i64, i64)
>  DEF_HELPER_FLAGS_2(xpaci, TCG_CALL_NO_RWG_SE, i64, env, i64)
>  DEF_HELPER_FLAGS_2(xpacd, TCG_CALL_NO_RWG_SE, i64, env, i64)
> +
> +DEF_HELPER_3(check_hcr_el2_trap, void, env, int, int)
> diff --git a/target/arm/internals.h b/target/arm/internals.h
> index f5313dd3d4..5a55e960de 100644
> --- a/target/arm/internals.h
> +++ b/target/arm/internals.h
> @@ -430,6 +430,14 @@ static inline uint32_t syn_simd_access_trap(int cv, int cond, bool is_16bit)
>          | (cv << 24) | (cond << 20) | (1 << 5);
>  }
>  
> +static inline uint32_t syn_vmrs_trap(int rt, int reg)
> +{
> +    return (EC_FPIDTRAP << ARM_EL_EC_SHIFT)
> +        | ARM_EL_IL
> +        | (1 << 24) | (0xe << 20) | (7 << 14)
> +        | (reg << 10) | (rt << 5) | 1;
> +}
> +
>  static inline uint32_t syn_sve_access_trap(void)
>  {
>      return EC_SVEACCESSTRAP << ARM_EL_EC_SHIFT;
> diff --git a/target/arm/translate-vfp.inc.c b/target/arm/translate-vfp.inc.c
> index 85c5ef897b..4c435b6c35 100644
> --- a/target/arm/translate-vfp.inc.c
> +++ b/target/arm/translate-vfp.inc.c
> @@ -759,15 +759,21 @@ static bool trans_VMSR_VMRS(DisasContext *s, arg_VMSR_VMRS *a)
>      }
>  
>      if (a->l) {
> +        TCGv_i32 tcg_rt, tcg_reg;
> +
>          /* VMRS, move VFP special register to gp register */
>          switch (a->reg) {
> +        case ARM_VFP_MVFR0:
> +        case ARM_VFP_MVFR1:
> +        case ARM_VFP_MVFR2:
>          case ARM_VFP_FPSID:
> +            tcg_rt = tcg_const_i32(a->rt);
> +            tcg_reg = tcg_const_i32(a->reg);
> +            gen_helper_check_hcr_el2_trap(cpu_env, tcg_rt, tcg_reg);
> +            /* fall through */
>          case ARM_VFP_FPEXC:
>          case ARM_VFP_FPINST:
>          case ARM_VFP_FPINST2:
> -        case ARM_VFP_MVFR0:
> -        case ARM_VFP_MVFR1:
> -        case ARM_VFP_MVFR2:
>              tmp = load_cpu_field(vfp.xregs[a->reg]);
>              break;
>          case ARM_VFP_FPSCR:
> diff --git a/target/arm/vfp_helper.c b/target/arm/vfp_helper.c
> index 9710ef1c3e..44e538e51c 100644
> --- a/target/arm/vfp_helper.c
> +++ b/target/arm/vfp_helper.c
> @@ -1322,4 +1322,31 @@ float64 HELPER(frint64_d)(float64 f, void *fpst)
>      return frint_d(f, fpst, 64);
>  }
>  
> +void HELPER(check_hcr_el2_trap)(CPUARMState *env, int rt, int reg)
> +{
> +    if (arm_current_el(env) != 1) {
> +        return;
> +    }

I think we could move the EL1 check to translation time, couldn't we?

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



> +
> +    switch (reg) {
> +    case ARM_VFP_MVFR0:
> +    case ARM_VFP_MVFR1:
> +    case ARM_VFP_MVFR2:
> +        if (!(arm_hcr_el2_eff(env) & HCR_TID3)) {
> +            return;
> +        }
> +        break;
> +    case ARM_VFP_FPSID:
> +        if (!(arm_hcr_el2_eff(env) & HCR_TID0)) {
> +            return;
> +        }
> +        break;
> +    default:
> +        /* Shouldn't be here... */
> +        return;
> +    }
> +
> +    raise_exception(env, EXCP_HYP_TRAP, syn_vmrs_trap(rt, reg), 2);
> +}
> +
>  #endif
> -- 
> 2.20.1
> 
>