Re: [PATCH v8 03/19] target/riscv/cpu.c: set satp_max_supported in cpu_riscv_set_satp()

[Daniel Henrique Barboza <dbarboza@ventanamicro.com>]

On 11/2/23 06:24, Andrew Jones wrote:
> On Wed, Nov 01, 2023 at 05:41:48PM -0300, Daniel Henrique Barboza wrote:
>> The setter() for the boolean attributes that set satp_mode (sv32, sv39,
>> sv48, sv57, sv64) considers that the CPU will always do a
>> set_satp_mode_max_supported() during cpu_init().
>>
>> This is not the case for the KVM 'host' CPU, and we'll add another CPU
>> that won't set satp_mode_max() during cpu_init(). Users should be able
>> to set a max_support in these circunstances.
>>
>> Allow cpu_riscv_set_satp() to set satp_mode_max_supported if the CPU
>> didn't set one prior.
>>
>> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>> ---
>>   target/riscv/cpu.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
>> index 822970345c..9f6837ecb7 100644
>> --- a/target/riscv/cpu.c
>> +++ b/target/riscv/cpu.c
>> @@ -1100,6 +1100,7 @@ static void cpu_riscv_get_satp(Object *obj, Visitor *v, const char *name,
>>   static void cpu_riscv_set_satp(Object *obj, Visitor *v, const char *name,
>>                                  void *opaque, Error **errp)
>>   {
>> +    RISCVCPU *cpu = RISCV_CPU(obj);
>>       RISCVSATPMap *satp_map = opaque;
>>       uint8_t satp = satp_mode_from_str(name);
>>       bool value;
>> @@ -1108,6 +1109,16 @@ static void cpu_riscv_set_satp(Object *obj, Visitor *v, const char *name,
>>           return;
>>       }
>>   
>> +    /*
>> +     * Allow users to set satp max supported if the CPU didn't
>> +     * set any during cpu_init(). First value set to 'true'
>> +     * in this case is assumed to be the max supported for
>> +     * the CPU.
> 
> Hmm, doesn't that mean if a user does
> 
>   -cpu rv64,sv39=true,sv48=true
> 
> then the max is set to sv39 instead of sv48?
> 
> I made a mistake in my last review by stating we shouldn't set the max
> supported satp for rv64i to the maximum satp that TCG supports. I forgot
> how all of it worked. Setting the _supported_ modes to the maximum that
> TCG supports makes sense as long as we don't default to any of them for
> rv64i. So, I think we should return the set_satp_mode_max_supported() to
> rv64i's definition (passing VM_1_10_SV57 or maybe even VM_1_10_SV64) and
> then change set_satp_mode_default_map() to error out for rv64i (or maybe
> for all "bare" type cpus).

Ok, then let's set max supported mode to SV64 (the maximum we allow).

Then we don't need to do anything else - setting a max supported value will allow
TCG to handle it accordingly with OpenSBI and the kernel, and a suitable satp_mode
will be picked by them. We can leave finalize() untouched.

I'll make a note in cpu_init() to remind ourselves that we're not setting a default
satp_mode value, but a *limit* for the satp_mode value the CPU can handle. This can be
done in the 'rv64i' patch.


Thanks,


Daniel




> 
>> +     */
>> +    if (value && cpu->cfg.satp_mode.supported == 0) {
>> +        set_satp_mode_max_supported(cpu, satp);
>> +    }
>> +
>>       satp_map->map = deposit32(satp_map->map, satp, 1, value);
>>       satp_map->init |= 1 << satp;
>>   }
>> -- 
>> 2.41.0
>>
> 
> Thanks,
> drew