Re: [PATCH v3 3/3] arm64/kvm: Fine grain _EL2 system registers list that affect nested virtualization

[Eric Auger]

Hi Marc,

On 10/12/23 22:36, Marc Zyngier wrote:
> On 2023-10-12 16:22, Eric Auger wrote:
>> Hi Miguel,
>>
>> On 10/11/23 20:01, Miguel Luis wrote:
>>> Implement a fine grained approach in the _EL2 sysreg ranges.
>>>
>>> Fixes: d0fc0a2519a6 ("KVM: arm64: nv: Add trap forwarding for HCR_EL2")
>>> Signed-off-by: Miguel Luis <miguel.luis@xxxxxxxxxx>
>>> ---
>>>  arch/arm64/kvm/emulate-nested.c | 88 ++++++++++++++++++++++++++++++---
>>>  1 file changed, 82 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/emulate-nested.c
>>> b/arch/arm64/kvm/emulate-nested.c
>>> index 9ced1bf0c2b7..3af49e130ee6 100644
>>> --- a/arch/arm64/kvm/emulate-nested.c
>>> +++ b/arch/arm64/kvm/emulate-nested.c
>>> @@ -648,15 +648,91 @@ static const struct encoding_to_trap_config
>>> encoding_to_cgt[] __initconst = {
>>>      SR_TRAP(SYS_APGAKEYLO_EL1,    CGT_HCR_APK),
>>>      SR_TRAP(SYS_APGAKEYHI_EL1,    CGT_HCR_APK),
>>>      /* All _EL2 registers */
>>> -    SR_RANGE_TRAP(sys_reg(3, 4, 0, 0, 0),
>>> -              sys_reg(3, 4, 3, 15, 7), CGT_HCR_NV),
>>> +    SR_TRAP(SYS_VPIDR_EL2,        CGT_HCR_NV),
>> I think you miss DBGVCR32_EL2
>
> I don't think this register should be part of this list. We don't
> support AArch32 with NV, and the spec says that DBGVCR32_EL2 UNDEFs
> when EL1 doesn't support AArch32.
>
> So the change that needs to happen is to inject an UNDEF when trapping
> a DBGVCR32_EL2and not forward the trap to the guest.

OK this makes sense

Thanks

Eric
>
> Thanks,
>
>         M.