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From: Oliver Upton To: Raghavendra Rao Ananta Cc: Marc Zyngier , Alexandru Elisei , James Morse , Suzuki K Poulose , Paolo Bonzini , Zenghui Yu , Shaoqin Huang , Jing Zhang , Reiji Watanabe , Colton Lewis , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v5 02/12] KVM: arm64: PMU: Set the default PMU for the guest on vCPU reset Message-ID: References: <20230817003029.3073210-1-rananta@google.com> <20230817003029.3073210-3-rananta@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230817003029.3073210-3-rananta@google.com> X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Aug 17, 2023 at 12:30:19AM +0000, Raghavendra Rao Ananta wrote: > From: Reiji Watanabe > > The following patches will use the number of counters information > from the arm_pmu and use this to set the PMCR.N for the guest > during vCPU reset. However, since the guest is not associated > with any arm_pmu until userspace configures the vPMU device > attributes, and a reset can happen before this event, call > kvm_arm_support_pmu_v3() just before doing the reset. > > No functional change intended. But there absolutely is a functional change here, and user visible at that. KVM_ARM_VCPU_INIT ioctls can now fail with -ENODEV, which is not part of the documented errors for the interface. > Signed-off-by: Reiji Watanabe > Signed-off-by: Raghavendra Rao Ananta > --- > arch/arm64/kvm/pmu-emul.c | 9 +-------- > arch/arm64/kvm/reset.c | 18 +++++++++++++----- > include/kvm/arm_pmu.h | 6 ++++++ > 3 files changed, 20 insertions(+), 13 deletions(-) > > diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c > index 0ffd1efa90c07..b87822024828a 100644 > --- a/arch/arm64/kvm/pmu-emul.c > +++ b/arch/arm64/kvm/pmu-emul.c > @@ -865,7 +865,7 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq) > return true; > } > > -static int kvm_arm_set_vm_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu) > +int kvm_arm_set_vm_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu) > { > lockdep_assert_held(&kvm->arch.config_lock); > > @@ -937,13 +937,6 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr) > if (vcpu->arch.pmu.created) > return -EBUSY; > > - if (!kvm->arch.arm_pmu) { > - int ret = kvm_arm_set_vm_pmu(kvm, NULL); > - > - if (ret) > - return ret; > - } > - > switch (attr->attr) { > case KVM_ARM_VCPU_PMU_V3_IRQ: { > int __user *uaddr = (int __user *)(long)attr->addr; > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c > index bc8556b6f4590..4c20f1ccd0789 100644 > --- a/arch/arm64/kvm/reset.c > +++ b/arch/arm64/kvm/reset.c > @@ -206,6 +206,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu) > */ > int kvm_reset_vcpu(struct kvm_vcpu *vcpu) > { > + struct kvm *kvm = vcpu->kvm; > struct vcpu_reset_state reset_state; > int ret; > bool loaded; > @@ -216,6 +217,18 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) > vcpu->arch.reset_state.reset = false; > spin_unlock(&vcpu->arch.mp_state_lock); > > + /* > + * When the vCPU has a PMU, but no PMU is set for the guest > + * yet, set the default one. > + */ > + if (kvm_vcpu_has_pmu(vcpu) && unlikely(!kvm->arch.arm_pmu)) { > + ret = -EINVAL; > + if (kvm_arm_support_pmu_v3()) > + ret = kvm_arm_set_vm_pmu(kvm, NULL); > + if (ret) > + return ret; > + } > + On top of my prior suggestion w.r.t. the default PMU helper, I'd rather see this block look like: if (kvm_vcpu_has_pmu(vcpu)) { if (!kvm_arm_support_pmu_v3()) return -EINVAL; /* * When the vCPU has a PMU but no PMU is set for the * guest yet, set the default one. */ if (unlikely(!kvm->arch.arm_pmu) && kvm_set_default_pmu(kvm)) return -EINVAL; } This would eliminate the possibility of returning ENODEV to userspace where we shouldn't. -- Thanks, Oliver