Paul Mackerras <paulus@xxxxxxxxxx> writes:
> 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.
I assume we don't have a KVM unit test that would have caught this?
cheers
