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

[Alexander Graf]

On 15.07.2013, at 16:04, Anup Patel wrote:

> 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.

So where does the v8 come from? Is there any non-ARMv8 XGene? If not, this is v1 really, right? What if we just call it v1 instead? Then when a new core comes up that needs different treatment, we create a new target.

But this really is Marc's call.


Alex