[PATCH v5 18/69] KVM: arm64: nv: Handle virtual EL2 registers in vcpu_read/write_sys_reg()

[Ganapatrao Kulkarni]

On 21-12-2021 02:09 pm, Marc Zyngier wrote:
> On Tue, 21 Dec 2021 07:12:36 +0000,
> Ganapatrao Kulkarni <gankulkarni at os.amperecomputing.com> wrote:
>>
>>
>>
>> On 20-12-2021 02:40 pm, Marc Zyngier wrote:
>>> On Mon, 20 Dec 2021 07:04:44 +0000,
>>> Ganapatrao Kulkarni <gankulkarni at os.amperecomputing.com> wrote:
>>>>
>>>>
>>>> On 30-11-2021 01:30 am, Marc Zyngier wrote:
>>>>> KVM internally uses accessor functions when reading or writing the
>>>>> guest's system registers. This takes care of accessing either the stored
>>>>> copy or using the "live" EL1 system registers when the host uses VHE.
>>>>>
>>>>> With the introduction of virtual EL2 we add a bunch of EL2 system
>>>>> registers, which now must also be taken care of:
>>>>> - If the guest is running in vEL2, and we access an EL1 sysreg, we must
>>>>>      revert to the stored version of that, and not use the CPU's copy.
>>>>> - If the guest is running in vEL1, and we access an EL2 sysreg, we must
>>>>
>>>> Do we have vEL1? or is it a typo?
>>>
>>> Not a typo, but only a convention (there is no such concept in the
>>> architecture). vELx denotes the exception level the guest thinks it is
>>> running at while running at EL1 (as it is the case for both vEL1 and
>>> vEL2).
>>>
>>
>> OK got it, this is to deal with Non-VHE case.
> 
> No, you'd have the exact same thing with a VHE guest itself running an
> EL1 guest. You really cannot distinguish the two cases.
> 
Okay understood, thanks.

> In general, you can't really think the NV support in terms of VHE or
> nVHE, or even in terms of guest level. You need to think in terms of a
> single machine with three exception levels, and follow the rules of
> the architecture to the letter.

OK.
> 
> Thanks,
> 
> 	M.
> 

Thanks,
Ganapat