Re: [PATCH 4/5] KVM: arm64: Limit the debug architecture to ARMv8.0

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Hi Marc,

On 16/02/2020 18:53, Marc Zyngier wrote:
> Let's not pretend we support anything but ARMv8.0 as far as the
> debug architecture is concerned.

(what happens for features that disappeared?)

For v8.0 the 'OS Double Lock' was mandatory. With v8.2 it became optional, and
not-implemented with v8.3.

The guest can see whether its implemented in ID_AA64DFR0_EL1. (and its 32bit friends)
Previously these values would have at least matched, even though KVM implements it as
RAZ/WI (which is the not-implemented behaviour).


Would anyone care that these are inconsistent?
(I've never had a solid grasp of how these debug 'lock' registers are supposed to be used).


Thanks,

James


> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 06b2d0dc6c73..43087b50a211 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1094,6 +1094,9 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
>  				 FEATURE(ID_AA64ISAR1_GPI));
>  		break;
>  	case SYS_ID_AA64DFR0_EL1:
> +		/* Limit debug to ARMv8.0 */
> +		val &= ~FEATURE(ID_AA64DFR0_DEBUGVER);
> +		val |= FIELD_PREP(FEATURE(ID_AA64DFR0_DEBUGVER), 6);
>  		/* Limit PMU to ARMv8.1 */
>  		val &= ~FEATURE(ID_AA64DFR0_PMUVER);
>  		val |= FIELD_PREP(FEATURE(ID_AA64DFR0_PMUVER), 4);
> 




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