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

[Jan Kiszka <jan.kiszka@siemens.com>]

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 <agraf@suse.de>
>>> ---
>>> 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.

> 
> 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.

Jan

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