Subject: Re: [PATCH 3/5] kvm: arm64: Limit PMU version to ARMv8.1

From: Marc Zyngier <[email-masked]>
Date: Wed, 19 Feb 2020 09:46:11 +0000

On 2020-02-18 17:43, James Morse wrote:
> Hi Marc,
> 
> On 16/02/2020 18:53, Marc Zyngier wrote:
>> Our PMU code is only implementing the ARMv8.1 features, so let's
>> stick to this when reporting the feature set to the guest.
> 
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index 682fedd7700f..06b2d0dc6c73 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -1093,6 +1093,11 @@ static u64 read_id_reg(const struct kvm_vcpu 
>> *vcpu,
>>  				 FEATURE(ID_AA64ISAR1_GPA) |
>>  				 FEATURE(ID_AA64ISAR1_GPI));
>>  		break;
>> +	case SYS_ID_AA64DFR0_EL1:
>> +		/* Limit PMU to ARMv8.1 */
> 
> Not just limit, but upgrade too! (force?)
> This looks safe because ARMV8_PMU_EVTYPE_EVENT always includes the
> extra bits this added, and the register is always trapped.

That's definitely not what I intended! Let me fix that one.

> The PMU version is also readable via ID_DFR0_EL1.PerfMon, should that
> be sanitised to be the same? (I don't think we've hidden an aarch64
> feature that also existed in aarch32 before).

Indeed, yet another oversight. I'll fix that too.

> Regardless:
> Reviewed-by: James Morse <[email-masked]>

You're way too kind! ;-)

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

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