Messages in this thread | | | From | Raghavendra Rao Ananta <> | Date | Tue, 17 Oct 2023 09:49:07 -0700 | Subject | Re: [PATCH v7 08/12] KVM: arm64: PMU: Allow userspace to limit PMCR_EL0.N for the guest |
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On Tue, Oct 17, 2023 at 8:52 AM Sebastian Ott <sebott@redhat.com> wrote: > > On Mon, 9 Oct 2023, Raghavendra Rao Ananta wrote: > > +static int set_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r, > > + u64 val) > > +{ > > + struct kvm *kvm = vcpu->kvm; > > + u64 new_n, mutable_mask; > > + > > + mutex_lock(&kvm->arch.config_lock); > > + > > + /* > > + * Make PMCR immutable once the VM has started running, but do > > + * not return an error (-EBUSY) to meet the existing expectations. > > + */ > > Why should we mention which error we're _not_ returning? > Oh, it's not to break the existing userspace expectations. Before this series, any 'write' from userspace was possible. Returning -EBUSY all of a sudden might tamper with this expectation.
Thank you. Raghavendra > > > + if (kvm_vm_has_ran_once(vcpu->kvm)) { > > + mutex_unlock(&kvm->arch.config_lock); > > + return 0; > > + } >
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