[PATCH v3 11/14] KVM: arm64: PMU: Allow ID_AA64DFR0_EL1.PMUver to be set from userspace

[Marc Zyngier]

On 2022-11-08 05:38, Reiji Watanabe wrote:
> Hi Marc,
> 
> On Mon, Nov 7, 2022 at 1:16 AM Marc Zyngier <maz at kernel.org> wrote:
>> 
>> Allow userspace to write ID_AA64DFR0_EL1, on the condition that only
>> the PMUver field can be altered and be at most the one that was
>> initially computed for the guest.
>> 
>> Signed-off-by: Marc Zyngier <maz at kernel.org>
>> ---
>>  arch/arm64/kvm/sys_regs.c | 40 
>> ++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 39 insertions(+), 1 deletion(-)
>> 
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index 7a4cd644b9c0..47c882401f3c 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -1247,6 +1247,43 @@ static int set_id_aa64pfr0_el1(struct kvm_vcpu 
>> *vcpu,
>>         return 0;
>>  }
>> 
>> +static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
>> +                              const struct sys_reg_desc *rd,
>> +                              u64 val)
>> +{
>> +       u8 pmuver, host_pmuver;
>> +       bool valid_pmu;
>> +
>> +       host_pmuver = kvm_arm_pmu_get_pmuver_limit();
>> +
>> +       /*
>> +        * Allow AA64DFR0_EL1.PMUver to be set from userspace as long
>> +        * as it doesn't promise more than what the HW gives us. We
>> +        * allow an IMPDEF PMU though, only if no PMU is supported
>> +        * (KVM backward compatibility handling).
>> +        */
>> +       pmuver = FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_EL1_PMUVer), 
>> val);
>> +       if ((pmuver != ID_AA64DFR0_EL1_PMUVer_IMP_DEF && pmuver > 
>> host_pmuver) ||
>> +           (pmuver != 0 && pmuver < ID_AA64DFR0_EL1_PMUVer_IMP))
> 
> Nit: Since this second condition cannot be true (right?), perhaps it 
> might
> be rather confusing?  I wasn't able to understand what it meant until
> I see the equivalent check in set_id_dfr0_el1() (Maybe just me 
> though:).

Ah, that's just me being tainted with the AArch32 version which
doesn't start at 1 for PMUv3. I'll drop it.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...