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Subject: Re: [Qemu-devel] [PATCH v4 21/29] target-ppc: Enable FSCR facility
	check for TAR
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To: Alexey Kardashevskiy <aik@ozlabs.ru>, qemu-devel@nongnu.org
Cc: qemu-ppc@nongnu.org, Alexander Graf <agraf@suse.de>

On 6/3/2014 4:27 AM, Alexey Kardashevskiy wrote:
> This makes user-privileged read/write fail if TAR facility is not enabled
> in FSCR.
> 
> Since this is the very first check for enabled in FSCR facility,
> this also adds gen_fscr_facility_check() for using in spr_write_tar()/
> spr_read_tar().
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  target-ppc/translate_init.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
> index 6f0c36b..9b83d56 100644
> --- a/target-ppc/translate_init.c
> +++ b/target-ppc/translate_init.c
> @@ -7275,6 +7275,21 @@ enum BOOK3S_CPU_TYPE {
>      BOOK3S_CPU_POWER8
>  };
>  
> +static void gen_fscr_facility_check(void *opaque, int facility_sprn, int bit,
> +                                    int sprn, int cause)
> +{
> +    TCGv_i32 t1 = tcg_const_i32(bit);
> +    TCGv_i32 t2 = tcg_const_i32(sprn);
> +    TCGv_i32 t3 = tcg_const_i32(cause);
> +
> +    gen_update_current_nip(opaque);
> +    gen_helper_fscr_facility_check(cpu_env, t1, t2, t3);
> +
> +    tcg_temp_free_i32(t3);
> +    tcg_temp_free_i32(t2);
> +    tcg_temp_free_i32(t1);
> +}
> +
>  static int check_pow_970 (CPUPPCState *env)
>  {
>      if (env->spr[SPR_HID0] & 0x01C00000) {
> @@ -7568,10 +7583,22 @@ static void gen_spr_power6_common(CPUPPCState *env)
>                   0x00000000);
>  }
>  
> +static void spr_read_tar(void *opaque, int gprn, int sprn)
> +{
> +    gen_fscr_facility_check(opaque, SPR_FSCR, FSCR_TAR, sprn, FSCR_IC_TAR);
> +    spr_read_generic(opaque, gprn, sprn);
> +}
> +
> +static void spr_write_tar(void *opaque, int sprn, int gprn)
> +{
> +    gen_fscr_facility_check(opaque, SPR_FSCR, FSCR_TAR, sprn, FSCR_IC_TAR);
> +    spr_write_generic(opaque, sprn, gprn);
> +}
> +
>  static void gen_spr_power8_tce_address_control(CPUPPCState *env)
>  {
>      spr_register(env, SPR_TAR, "TAR",
> -                 &spr_read_generic, &spr_write_generic,
> +                 &spr_read_tar, &spr_write_tar,
>                   &spr_read_generic, &spr_write_generic,
>                   0x00000000);
>  }
> 

There are potential impacts to user mode here.  If I am reading correctly, TAR would not be accessible
in user mode.

An obvious fix would be to initialize FSCR to enable TAR access in the user mode build targets.