Re: [Qemu-devel] [PATCH v4 21/29] target-ppc: Enable FSCR facility check for TAR

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 06/04/2014 03:08 AM, Tom Musta wrote:
> 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.


And this is bad why exactly? I definitely need to learn about linux-user
more...


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


Like that?

 static void gen_spr_power8_fscr(CPUPPCState *env)
 {
+#if defined(CONFIG_USER_ONLY)
+    target_ulong initval = 1ULL << FSCR_TAR;
+#else
+    target_ulong initval = 0;
+#endif
     spr_register_kvm(env, SPR_FSCR, "FSCR",
                      SPR_NOACCESS, SPR_NOACCESS,
                      &spr_read_generic, &spr_write_generic,
-                     KVM_REG_PPC_FSCR, 0x00000000);
+                     KVM_REG_PPC_FSCR, initval);
 }


-- 
Alexey