[PATCH 7/9] KVM: arm64: PMU: Allow ID_AA64DFR0_EL1.PMUver to be set from userspace

[Oliver Upton]

Hi Marc,

On Fri, Aug 05, 2022 at 02:58:11PM +0100, Marc Zyngier 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.

As DFR0_EL1 is exposed to userspace, isn't a ->set_user() hook required
for it as well?

> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 55451f49017c..c0595f31dab8 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1236,6 +1236,38 @@ 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;
> +
> +	host_pmuver = kvm_arm_pmu_get_host_pmuver();
> +
> +	/*
> +	 * Allow AA64DFR0_EL1.PMUver to be set from userspace as long
> +	 * as it doesn't promise more than what the HW gives us. We
> +	 * don't allow an IMPDEF PMU though.
> +	 */
> +	pmuver = FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER), val);
> +	if (pmuver == ID_AA64DFR0_PMUVER_IMP_DEF || pmuver > host_pmuver)
> +		return -EINVAL;
> +
> +	/* We already have a PMU, don't try to disable it... */
> +	if (kvm_vcpu_has_pmu(vcpu) && pmuver == 0)
> +		return -EINVAL;
> +
> +	/* We can only differ with PMUver, and anything else is an error */
> +	val ^= read_id_reg(vcpu, rd, false);
> +	val &= ~(0xFUL << ID_AA64DFR0_PMUVER_SHIFT);

nit: ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER)

--
Thanks,
Oliver