Re: [PATCH v8 07/13] KVM: arm64: PMU: Allow userspace to limit PMCR_EL0.N for the guest

[Oliver Upton]

On Fri, Oct 20, 2023 at 09:40:47PM +0000, Raghavendra Rao Ananta wrote:

[...]

> +	/*
> +	 * Make PMCR immutable once the VM has started running, but
> +	 * do not return an error to meet the existing expectations.
> +	 */
> +	if (kvm_vm_has_ran_once(vcpu->kvm)) {
> +		mutex_unlock(&kvm->arch.config_lock);
> +		return 0;
> +	}

Marc pointed out offline that PMCR_EL0 needs to be mutable at runtime as
well. I'll admit, the architecture isn't very helpful as it is both used
for identification _and_ configuration.

What I had in mind a few revisions ago when I gave the suggestion was to
ignore writes to _just_ the PMCR_EL0.N field after the VM has started.

-- 
Thanks,
Oliver