[PATCH] arm64: KVM: Support X-Gene guest VCPU on APM X-Gene host

[Anup Patel]

On Mon, Jul 15, 2013 at 6:32 PM, Alexander Graf <agraf at suse.de> wrote:
>
> On 15.07.2013, at 14:56, Anup Patel wrote:
>
>> Hi Marc,
>>
>> On Mon, Jul 15, 2013 at 6:09 PM, Marc Zyngier <marc.zyngier at arm.com> wrote:
>>> Hi Anup,
>>>
>>> On 15/07/13 12:46, Anup Patel wrote:
>>>> This patch allows us to have X-Gene guest VCPU when using
>>>> KVM arm64 on APM X-Gene host.
>>>>
>>>> We add KVM_ARM_TARGET_XGENE_V8 for X-Gene compatible guest VCPU
>>>> and we return KVM_ARM_TARGET_XGENE_V8 in kvm_target_cpu() when
>>>> running on X-Gene host.
>>>>
>>>> Signed-off-by: Anup Patel <anup.patel at linaro.org>
>>>> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar at linaro.org>
>>>> ---
>>>> arch/arm64/include/uapi/asm/kvm.h    |    3 ++-
>>>> arch/arm64/kvm/guest.c               |   34 ++++++++++++++++++++++------------
>>>> arch/arm64/kvm/sys_regs_generic_v8.c |    3 +++
>>>> 3 files changed, 27 insertions(+), 13 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
>>>> index 5031f42..8194707 100644
>>>> --- a/arch/arm64/include/uapi/asm/kvm.h
>>>> +++ b/arch/arm64/include/uapi/asm/kvm.h
>>>> @@ -55,8 +55,9 @@ struct kvm_regs {
>>>> #define KVM_ARM_TARGET_AEM_V8                0
>>>> #define KVM_ARM_TARGET_FOUNDATION_V8 1
>>>> #define KVM_ARM_TARGET_CORTEX_A57    2
>>>> +#define KVM_ARM_TARGET_XGENE_V8              3
>>>>
>>>> -#define KVM_ARM_NUM_TARGETS          3
>>>> +#define KVM_ARM_NUM_TARGETS          4
>>>>
>>>> /* KVM_ARM_SET_DEVICE_ADDR ioctl id encoding */
>>>> #define KVM_ARM_DEVICE_TYPE_SHIFT    0
>>>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
>>>> index 2c3ff67..e99b0a5 100644
>>>> --- a/arch/arm64/kvm/guest.c
>>>> +++ b/arch/arm64/kvm/guest.c
>>>> @@ -207,19 +207,29 @@ int __attribute_const__ kvm_target_cpu(void)
>>>>      unsigned long implementor = read_cpuid_implementor();
>>>>      unsigned long part_number = read_cpuid_part_number();
>>>>
>>>> -     if (implementor != ARM_CPU_IMP_ARM)
>>>> -             return -EINVAL;
>>>> -
>>>> -     switch (part_number) {
>>>> -     case ARM_CPU_PART_AEM_V8:
>>>> -             return KVM_ARM_TARGET_AEM_V8;
>>>> -     case ARM_CPU_PART_FOUNDATION:
>>>> -             return KVM_ARM_TARGET_FOUNDATION_V8;
>>>> -     case ARM_CPU_PART_CORTEX_A57:
>>>> -             /* Currently handled by the generic backend */
>>>> -             return KVM_ARM_TARGET_CORTEX_A57;
>>>> +     switch (implementor) {
>>>> +     case ARM_CPU_IMP_ARM:
>>>> +             switch (part_number) {
>>>> +             case ARM_CPU_PART_AEM_V8:
>>>> +                     return KVM_ARM_TARGET_AEM_V8;
>>>> +             case ARM_CPU_PART_FOUNDATION:
>>>> +                     return KVM_ARM_TARGET_FOUNDATION_V8;
>>>> +             case ARM_CPU_PART_CORTEX_A57:
>>>> +                     return KVM_ARM_TARGET_CORTEX_A57;
>>>> +             default:
>>>> +                     return -EINVAL;
>>>> +             }
>>>> +             break;
>>>> +     case ARM_CPU_IMP_APM:
>>>> +             switch (part_number) {
>>>> +             case APM_CPU_PART_POTENZA:
>>>> +                     return KVM_ARM_TARGET_XGENE_V8;
>>>
>>> Why don't we have KVM_ARM_TARGET_XGENE_POTENZA (or something similar)
>>> instead? I don't expect all the X-Gene CPUs to be the same forever...
>>
>> OK, I will rename it to KVM_ARM_TARGET_XGENE_POTENZA.
>>
>> Does this mean that with every new ARM64 CPU we will have to add a new
>> target for KVM ARM64 ?
>
> Only for different core types, no? Any Cortex-A57 should still behave the same.
>
>> If so then I think the list of targets will grow very fast.
>>
>> I also realized that if we add a new target type in KVM ARM64 then we have
>> to also update KVMTOOL to use the new target else KVMTOOL fails to
>> recognize the target provided by KVM ARM64.
>
> Right. It might make sense to have a fetch mechanism for the host cpu part. So you can ask KVM for the host cpu type and pass that back in here.
>
>> Do you think we can have KVM_ARM_TARGET_xxx to represent a common
>> target for a family of CPUs from given ARM64 vendor?
>
> Anything that is compatible is compatible :). I don't know the product roadmaps for X-Gene cores, but you will want to make the field here as coarse grained as possible, while maintaining the guarantee that a guest still behaves the same.

Actually, I don't see X-Gene cores changing in-terms of register interface
available to EL1 and EL0 in near future. This is the reason why I had named
the target as KVM_ARM_TARGET_XGENE_V8.

My only concern in having a more specific target type (such as
KVM_ARM_TARGET_XGENE_POTENZA) is that we might unnecessarily
add new target types without any difference on KVM-side.

>
>
> Alex
>

--Anup