Re: [Qemu-devel] Minimal ARM LPAE support

[Alexey Starikovskiy <aystarik@gmail.com>]

On 03/13/2012 06:21 PM, Peter Maydell wrote:
> On 13 March 2012 11:19, Alexey Starikovskiy<aystarik@gmail.com>  wrote:
>> Minimal ARM LPAE support. Sufficient to boot Linux kernel on vexpress-a15
> This is missing chunks of what LPAE ought to mean, which is dubious,
> and it doesn't state clearly what it is missing, which is definitely
> a problem.
>
I've cut out Virtualization, TrustZone, shareable/cache attributes.
Also, as you've mentioned later, phys_address is still 32 bits, so we really can't get more memory than before.
>> +void HELPER(set_cp15_64)(CPUState *env, uint32_t insn, uint64_t val)
>> +{
>> +    int crm = insn&  0xf;
>> +    int opc1 = (insn>>  4)&  0xf;
>> +    if (crm == 2) {
>> +        switch (opc1) {
>> +        case 0:
>> +            env->cp15.c2_base0 = val;
>> +            tlb_flush(env, 0); // might change ASID
>> +            return;
>> +        case 1:
>> +            env->cp15.c2_base1 = val;
>> +            tlb_flush(env, 0); // might change ASID
>> +            return;
>> +        default:;
>> +        }
>> +    } else if (crm == 7) {
>> +        if (opc1 == 0) {
>> +            env->cp15.c7_par = val;
>> +            return;
>> +        }
>> +    }
>> +    cpu_abort(env, "Unimplemented cp15 register 64bit write (c%d[%d])\n",
>> crm, opc1);
>> +}
> This is aiming 64 bit cp15 handling for the same swamp in which
> 32 bit cp15 is currently stuck. At a bare minimum, this must do
> complete decoding of all the crn/crm/opc fields, and must restrict
> register implementations to only CPUs where they exist (ie check
> ARM_FEATURE_LPAE).
>
As it is a helper for MCRR, only crm and opc1 fields are present in instruction. All allowed values are checked.
I'll need to check how MCRR to these registers will behave if LPAE is not featured
>> --- a/target-arm/translate.c
>> +++ b/target-arm/translate.c
>> @@ -2559,17 +2559,9 @@ static int disas_cp15_insn(CPUState *env,
>> DisasContext *s, uint32_t insn)
>>
>>      /* M profile cores use memory mapped registers instead of cp15.  */
>>      if (arm_feature(env, ARM_FEATURE_M))
>> -    return 1;
>> +        return 1;
>>
>> -    if ((insn&  (1<<  25)) == 0) {
>> -        if (insn&  (1<<  20)) {
>> -            /* mrrc */
>> -            return 1;
>> -        }
>> -        /* mcrr.  Used for block cache operations, so implement as no-op.
>>   */
> This change seems to drop the MCRR block cache op handling and I don't
> see anything elsewhere which implements it. This will presumably break
> some CPU/guest combination.
Do you have any pointer on that exactly did we try to emulate here?
> More general question -- should we move target_phys_addr_t to a 64
> bit type?
It could be done later on, for now it works as is. Making it 64 bit breaks DMA in pxa*, so I'm not sure how to do that properly.

Thanks,
Alex.