> On 21-Jul-2020, at 9:24 AM, Paul Mackerras <paulus@ozlabs.org> wrote:
> 
> On Fri, Jul 17, 2020 at 10:38:14AM -0400, Athira Rajeev wrote:
>> Currently `kvm_vcpu_arch` stores all Monitor Mode Control registers
>> in a flat array in order: mmcr0, mmcr1, mmcra, mmcr2, mmcrs
>> Split this to give mmcra and mmcrs its own entries in vcpu and
>> use a flat array for mmcr0 to mmcr2. This patch implements this
>> cleanup to make code easier to read.
> 
> Changing the way KVM stores these values internally is fine, but
> changing the user ABI is not.  This part:
> 
>> diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
>> index 264e266..e55d847 100644
>> --- a/arch/powerpc/include/uapi/asm/kvm.h
>> +++ b/arch/powerpc/include/uapi/asm/kvm.h
>> @@ -510,8 +510,8 @@ struct kvm_ppc_cpu_char {
>> 
>> #define KVM_REG_PPC_MMCR0	(KVM_REG_PPC | KVM_REG_SIZE_U64 | 0x10)
>> #define KVM_REG_PPC_MMCR1	(KVM_REG_PPC | KVM_REG_SIZE_U64 | 0x11)
>> -#define KVM_REG_PPC_MMCRA	(KVM_REG_PPC | KVM_REG_SIZE_U64 | 0x12)
>> -#define KVM_REG_PPC_MMCR2	(KVM_REG_PPC | KVM_REG_SIZE_U64 | 0x13)
>> +#define KVM_REG_PPC_MMCR2	(KVM_REG_PPC | KVM_REG_SIZE_U64 | 0x12)
>> +#define KVM_REG_PPC_MMCRA	(KVM_REG_PPC | KVM_REG_SIZE_U64 | 0x13)
> 
> means that existing userspace programs that used to work would now be
> broken.  That is not acceptable (breaking the user ABI is only ever
> acceptable with a very compelling reason).  So NAK to this part of the
> patch.

Hi Paul

Thanks for checking the patch. I understood your point on user ABI breakage that this particular change can cause.
I will retain original KVM_REG_PPC_MMCRA and KVM_REG_PPC_MMCR2 order in `kvm.h`
And with that, additionally I will need below change ( on top of current patch ) for my clean up updates for kvm cpu MMCR to work,
Because now mmcra and mmcrs will have its own entries in vcpu and is not part of the mmcr[] array
Please suggest if this looks good

Thanks
Athira 

—
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 3f90eee261fc..b10bb404f0d5 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1679,10 +1679,13 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
        case KVM_REG_PPC_UAMOR:
                *val = get_reg_val(id, vcpu->arch.uamor);
                break;
-       case KVM_REG_PPC_MMCR0 ... KVM_REG_PPC_MMCR2:
+       case KVM_REG_PPC_MMCR0 ... KVM_REG_PPC_MMCR1:
                i = id - KVM_REG_PPC_MMCR0;
                *val = get_reg_val(id, vcpu->arch.mmcr[i]);
                break;
+       case KVM_REG_PPC_MMCR2:
+               *val = get_reg_val(id, vcpu->arch.mmcr[2]);
+               break;
        case KVM_REG_PPC_MMCRA:
                *val = get_reg_val(id, vcpu->arch.mmcra);
                break;
@@ -1906,10 +1909,13 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
        case KVM_REG_PPC_UAMOR:
                vcpu->arch.uamor = set_reg_val(id, *val);
                break;
-       case KVM_REG_PPC_MMCR0 ... KVM_REG_PPC_MMCR2:
+       case KVM_REG_PPC_MMCR0 ... KVM_REG_PPC_MMCR1:
                i = id - KVM_REG_PPC_MMCR0;
                vcpu->arch.mmcr[i] = set_reg_val(id, *val);
                break;
+       case KVM_REG_PPC_MMCR2:
+               vcpu->arch.mmcr[2] = set_reg_val(id, *val);
+               break;
        case KVM_REG_PPC_MMCRA:
                vcpu->arch.mmcra = set_reg_val(id, *val);
                break;
—


> 
> Regards,
> Paul.