[Qemu-devel] Re: [PATCH] PPC: Get MMU state on register sync

[Alexander Graf]

On 24.11.2009, at 19:33, Jan Kiszka wrote:

> Alexander Graf wrote:
>> On 24.11.2009, at 19:12, Jan Kiszka wrote:
>> 
>>> Alexander Graf wrote:
>>>> On 24.11.2009, at 19:01, Jan Kiszka wrote:
>>>> 
>>>>> Alexander Graf wrote:
>>>>>> While x86 only needs to sync cr0-4 to know all about its MMU state and 
>>>>>> enable
>>>>>> qemu to resolve virtual to physical addresses, we need to sync all of the
>>>>>> segment registers on PPC to know which mapping we're in.
>>>>>> 
>>>>>> So let's grab the segment register contents to be able to use the "x" 
>>>>>> monitor
>>>>>> command and also enable the gdbstub to resolve virtual addresses.
>>>>>> 
>>>>>> I sent the corresponding KVM patch to the KVM ML some minutes ago.
>>>>>> 
>>>>>> Signed-off-by: Alexander Graf <address@hidden>
>>>>>> ---
>>>>>> target-ppc/kvm.c |   30 ++++++++++++++++++++++++++++++
>>>>>> 1 files changed, 30 insertions(+), 0 deletions(-)
>>>>>> 
>>>>>> diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
>>>>>> index 4e1c65f..566513f 100644
>>>>>> --- a/target-ppc/kvm.c
>>>>>> +++ b/target-ppc/kvm.c
>>>>>> @@ -98,12 +98,17 @@ int kvm_arch_put_registers(CPUState *env)
>>>>>> int kvm_arch_get_registers(CPUState *env)
>>>>>> {
>>>>>>   struct kvm_regs regs;
>>>>>> +    struct kvm_sregs sregs;
>>>>>>   uint32_t i, ret;
>>>>>> 
>>>>>>   ret = kvm_vcpu_ioctl(env, KVM_GET_REGS, &regs);
>>>>>>   if (ret < 0)
>>>>>>       return ret;
>>>>>> 
>>>>>> +    ret = kvm_vcpu_ioctl(env, KVM_GET_SREGS, &sregs);
>>>>>> +    if (ret < 0)
>>>>>> +        return ret;
>>>>>> +
>>>>>>   env->ctr = regs.ctr;
>>>>>>   env->lr = regs.lr;
>>>>>>   env->xer = regs.xer;
>>>>>> @@ -125,6 +130,31 @@ int kvm_arch_get_registers(CPUState *env)
>>>>>>   for (i = 0;i < 32; i++)
>>>>>>       env->gpr[i] = regs.gpr[i];
>>>>>> 
>>>>>> +#ifdef KVM_CAP_PPC_SEGSTATE
>>>>>> +    if (kvm_check_extension(env->kvm_state, KVM_CAP_PPC_SEGSTATE)) {
>>>>>> +        env->sdr1 = sregs.sdr1;
>>>>>> +    
>>>>>> +        /* Sync SLB */
>>>>>> +        for (i = 0; i < 64; i++) {
>>>>>> +            ppc_store_slb(env, sregs.ppc64.slb[i].slbe,
>>>>>> +                               sregs.ppc64.slb[i].slbv);
>>>>>> +        }
>>>>>> +    
>>>>>> +        /* Sync SRs */
>>>>>> +        for (i = 0; i < 16; i++) {
>>>>>> +            env->sr[i] = sregs.ppc32.sr[i];
>>>>>> +        }
>>>>>> +    
>>>>>> +        /* Sync BATs */
>>>>>> +        for (i = 0; i < 8; i++) {
>>>>>> +            env->DBAT[0][i] = sregs.ppc32.dbat[i] & 0xffffffff;
>>>>>> +            env->DBAT[1][i] = sregs.ppc32.dbat[i] >> 32;
>>>>>> +            env->IBAT[0][i] = sregs.ppc32.ibat[i] & 0xffffffff;
>>>>>> +            env->IBAT[1][i] = sregs.ppc32.ibat[i] >> 32;
>>>>>> +        }
>>>>>> +    }
>>>>>> +#endif
>>>>>> +
>>>>>>   return 0;
>>>>>> }
>>>>>> 
>>>>> What about KVM_SET_SREGS in kvm_arch_put_registers? E.g. to play back
>>>>> potential changes to that special registers someone did via gdb?
>>>> I don't think you can actually change the segment values. At least I can't 
>>>> imagine why.
>>> Dunno about PPC in this regard and how much value it has, but we have
>>> segment register access via gdb for x86.
>> 
>> The segments here are more like PLM4 on x86.
> 
> Even that will be settable one day (gdb just do not yet know much about
> x86 system management registers).
> 
>> 
>>>> I definitely will implement SET_SREGS as soon as your sync split is in, as 
>>>> that's IMHO only really required on migration.
>>>> 
>>> Migration is, of course, the major use case.
>>> 
>>> Still I wonder why not making this API symmetric when already touching it.
>> 
>> I was afraid to introduce performance regressions - setting the segments 
>> means flushing the complete shadow MMU.
>> 
> 
> Unless it costs milliseconds, not really critical, given how often
> registers are synchronized.
> 
> BTW, I noticed that ppc only syncs the SREGS once on init, not on reset
> - are they static?

So far SREGS are only used for setting the PVR (cpuid in x86 speech). There's 
no need to reset that on reset :-).


Alex