Re: [RFC PATCH 1/2] KVM: arm64: nv: selftests: Add guest hypervisor test

[Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>]

On 07-02-2025 10:16 pm, Ganapatrao Kulkarni wrote:
> 
> 
> On 07-02-2025 07:29 pm, Marc Zyngier wrote:
>> On Fri, 07 Feb 2025 13:26:41 +0000,
>> Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com> wrote:
>>>
>>>>> +    if (is_vcpu_nested(vcpu)) {
>>>>> +        vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_CPTR_EL2), fpen);
>>>>> +        vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_SCTLR_EL2), 
>>>>> sctlr_el1);
>>>>> +        vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TCR_EL2), tcr_el1);
>>>>> +        vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MAIR_EL2), 
>>>>> DEFAULT_MAIR_EL1);
>>>>> +        vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TTBR0_EL2), 
>>>>> ttbr0_el1);
>>>>> +        vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TPIDR_EL2), vcpu- 
>>>>> >id);
>>>>
>>>> How about some of the basics such as HCR_EL2, MDCR_EL2? A bunch of
>>>> things there do have an impact on how the guest behaves, and relying
>>>> on defaults feels like a bad idea.
>>>
>>> Sure, I will try to have these registers also set to required value
>>> explicitly.
>>>
>>>>
>>>> This also assumes VHE, without trying to enforce it.
>>>
>>> Ok, I will try to set specific bits of HCR_EL2 to force it run in VHE.
>>>
>>>>
>>>> Finally, how to you plan to make all the existing tests run as EL2
>>>> guests if TPIDR_EL1 isn't populated with the expected value? Surely
>>>> you need to change the read side...
>>>

IIUC, we need not write to TPIDR_EL2, instead write always to TPIDR_EL1 
and in guest code(like function cpu_copy_el2regs in Linux kernel) copy 
TPIDR_EL1 value to TPIDR_EL2.

OR, Write to both TPIDR_EL1 and TPIDR_EL2 in the test code itself during 
vcpu setup.

-- 
Thanks,
Ganapat/GK