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From: Oliver Upton To: Shameer Kolothum Cc: kvmarm@lists.linux.dev, iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linuxarm@huawei.com, kevin.tian@intel.com, jgg@ziepe.ca, alex.williamson@redhat.com, maz@kernel.org, will@kernel.org, robin.murphy@arm.com, jean-philippe@linaro.org, jonathan.cameron@huawei.com Subject: Re: [RFC PATCH v2 2/7] KVM: arm64: Introduce support to pin VMIDs Message-ID: References: <20240208151837.35068-1-shameerali.kolothum.thodi@huawei.com> <20240208151837.35068-3-shameerali.kolothum.thodi@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240208151837.35068-3-shameerali.kolothum.thodi@huawei.com> X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240624_122230_624432_520E435E X-CRM114-Status: GOOD ( 15.46 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Shameer, On Thu, Feb 08, 2024 at 03:18:32PM +0000, Shameer Kolothum wrote: [...] > +unsigned long kvm_arm_pinned_vmid_get(struct kvm_vmid *kvm_vmid) > +{ > + unsigned long flags; > + u64 vmid; > + > + if (!pinned_vmid_map) > + return 0; Like I'd mentioned over in the other thread, returning 0 for error conditions is rather confusing unless one is staring at the VMID allocator code. Can you rework this to return an actual error (e.g. -EINVAL) on failure? > + raw_spin_lock_irqsave(&cpu_vmid_lock, flags); > + > + vmid = atomic64_read(&kvm_vmid->id); > + > + if (refcount_inc_not_zero(&kvm_vmid->pinned)) > + goto out_unlock; > + > + if (nr_pinned_vmids >= max_pinned_vmids) { > + vmid = 0; > + goto out_unlock; > + } You need to decrement the refcount in this error path. > + > + /* > + * If we went through one or more rollover since that VMID was > + * used, make sure it is still valid, or generate a new one. > + */ > + if (!vmid_gen_match(vmid)) > + vmid = new_vmid(kvm_vmid); > + > + nr_pinned_vmids++; > + __set_bit(vmid2idx(vmid), pinned_vmid_map); > + refcount_set(&kvm_vmid->pinned, 1); > + > +out_unlock: > + raw_spin_unlock_irqrestore(&cpu_vmid_lock, flags); > + > + vmid &= ~VMID_MASK; > + > + return vmid; > +} > + > +void kvm_arm_pinned_vmid_put(struct kvm_vmid *kvm_vmid) > +{ > + unsigned long flags; > + u64 vmid = atomic64_read(&kvm_vmid->id); > + > + if (!pinned_vmid_map) > + return; > + > + raw_spin_lock_irqsave(&cpu_vmid_lock, flags); > + > + if (refcount_dec_and_test(&kvm_vmid->pinned)) { > + __clear_bit(vmid2idx(vmid), pinned_vmid_map); > + nr_pinned_vmids--; > + } > + > + raw_spin_unlock_irqrestore(&cpu_vmid_lock, flags); > +} > + > /* > * Initialize the VMID allocator > */ > @@ -191,10 +263,20 @@ int __init kvm_arm_vmid_alloc_init(void) > if (!vmid_map) > return -ENOMEM; > > + pinned_vmid_map = bitmap_zalloc(NUM_USER_VMIDS, GFP_KERNEL); > + nr_pinned_vmids = 0; > + > + /* > + * Ensure we have at least one emty slot available after rollover typo: empty -- Thanks, Oliver