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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id by23sm3167995ejc.85.2021.06.17.04.23.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Jun 2021 04:23:39 -0700 (PDT) Subject: Re: [PATCH v10 2/5] KVM: stats: Add fd-based API to read binary stats data To: Greg KH , Jing Zhang References: <20210617044146.2667540-1-jingzhangos@google.com> <20210617044146.2667540-3-jingzhangos@google.com> From: Paolo Bonzini Message-ID: Date: Thu, 17 Jun 2021 13:23:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Cc: KVM , David Hildenbrand , Paul Mackerras , Linuxkselftest , Claudio Imbrenda , Will Deacon , KVMARM , Emanuele Giuseppe Esposito , LinuxS390 , Janosch Frank , Marc Zyngier , Huacai Chen , Christian Borntraeger , Aleksandar Markovic , David Rientjes , KVMPPC , Krish Sadhukhan , David Matlack , Jim Mattson , Thomas Bogendoerfer , Sean Christopherson , Cornelia Huck , Peter Shier , LinuxMIPS , Vitaly Kuznetsov X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On 17/06/21 09:03, Greg KH wrote: >> 3. Fd-based solution provides the possibility that a telemetry can >> read KVM stats in a less privileged situation. > "possiblity"? Does this work or not? Have you tested it? > I think this is essentially s/that/for/. But more precisely: 3. Compared for example to a ioctl, a separate file descriptor makes it possible for an external program to read statistics, while maintaining privilege separation between VMM and telemetry code. >> >> + snprintf(&kvm_vm_stats_header.id[0], sizeof(kvm_vm_stats_header.id), >> + "kvm-%d", task_pid_nr(current)); > > Why do you write to this static variable for EVERY read? Shouldn't you > just do it once at open? How can it change? > > Wait, it's a single shared variable, what happens when multiple tasks > open this thing and read from it? You race between writing to this > variable here and then: > >> + return kvm_stats_read(&kvm_vm_stats_header, &kvm_vm_stats_desc[0], >> + &kvm->stat, sizeof(kvm->stat), user_buffer, size, offset); > > Accessing it here. > > So how is this really working? It's not - Jing, kvm_vm_stats_header is small enough that you can store a copy in struct kvm. Paolo _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm