From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3BE3C3A59E for ; Mon, 4 Apr 2022 21:23:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1381084AbiDDVWY (ORCPT ); Mon, 4 Apr 2022 17:22:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49044 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1379542AbiDDR1S (ORCPT ); Mon, 4 Apr 2022 13:27:18 -0400 Received: from mail-pj1-x1032.google.com (mail-pj1-x1032.google.com [IPv6:2607:f8b0:4864:20::1032]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9ABD924BF9 for ; Mon, 4 Apr 2022 10:25:22 -0700 (PDT) Received: by mail-pj1-x1032.google.com with SMTP id g15-20020a17090adb0f00b001caa9a230c7so2343197pjv.5 for ; Mon, 04 Apr 2022 10:25:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=mgnV7xI4qUCKfrqlWFwfqK4AIab4DaYNplYu5ZnU12A=; b=h6IOoYbeGqsTOT85hNSp30Z6S3z/0oyrH77ylDcQCzYqAx2ZHRLm2YfmqSFB6NClJu kJcZx7FPEq1+GT1+BVhpf6hwXjOBLbp1YTYM8YeAerFOwniYHATjFWcncbG6zs4uc6lH D88N/qv4s8ZVGSl86KP8gRLyF0TEI/eJIvNpSlCtRlVqEnCJ37G+eGGqZ6VKZiksrR7/ f975k9mhAdFYWZ6szHTXhJ8FN8tFh7MppB6ZV6jJSdiwgzfuf9i/XV/f4wxmXlEauKwx Jdu6TE4dO0MoCr/z3O/HM6LiRiNFGaXRzJlLG1c4sNEbtr1FVbATJkiOaKRHQaYmNWJG QSpw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=mgnV7xI4qUCKfrqlWFwfqK4AIab4DaYNplYu5ZnU12A=; b=zqrR6eAhzB4pWfIAvbOSd8PCEWls3K+OQmC8TMC/kQwdPPZyoIFxpAENW9vf27r93d FepZc8/Y4A5H1+U9dt7Yf/fF17GDhN1As3dynxK8b924ZQ+YziUN9z91L5YjfeJmxA4D cisHBasA+bJNc1hZ2Ou8mfZK8LFacjQ12wWVIPGSndokRCM6EA3Y+r4B6anT8tq+rsjZ zV1Vkqex8atthqjGYMqnlS5KZqQVvIFdNDLKwrnj6vAu+EFK2tfVAQRWdQtW1Poj2Fc3 mMMy+DdlMMYnqCZU0aXTV9OM4PSZ7VwNXYd5g5iQhSeiZhf+hBKa+j1q6KJrZ3FWpGGN 2UrQ== X-Gm-Message-State: AOAM532nw9CuRWam5037Z1MJba0wKL2GJKFqsoE1zB2cU5WyJ8ncWqOa rG1uHrHbg/rjQQNnjQOxopURiQ== X-Google-Smtp-Source: ABdhPJyLI0a6Ip/thHpTPRIhpEWNh1fk6lFS2o3mWz/SM4TxmeP+4fejjowg5XpABQqXkGYoEg44EQ== X-Received: by 2002:a17:90b:38cd:b0:1ca:64dd:4747 with SMTP id nn13-20020a17090b38cd00b001ca64dd4747mr232081pjb.55.1649093121770; Mon, 04 Apr 2022 10:25:21 -0700 (PDT) Received: from google.com (157.214.185.35.bc.googleusercontent.com. [35.185.214.157]) by smtp.gmail.com with ESMTPSA id bx22-20020a056a00429600b004fa936a64b0sm12144176pfb.196.2022.04.04.10.25.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Apr 2022 10:25:20 -0700 (PDT) Date: Mon, 4 Apr 2022 17:25:17 +0000 From: Sean Christopherson To: Zeng Guang Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , "kvm@vger.kernel.org" , Dave Hansen , "Luck, Tony" , Kan Liang , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Kim Phillips , Jarkko Sakkinen , Jethro Beekman , "Huang, Kai" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "Hu, Robert" , "Gao, Chao" Subject: Re: [PATCH v7 7/8] KVM: x86: Allow userspace set maximum VCPU id for VM Message-ID: References: <20220304080725.18135-1-guang.zeng@intel.com> <20220304080725.18135-8-guang.zeng@intel.com> <60879468-c54f-e7f1-2123-ba4cf4128ac3@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <60879468-c54f-e7f1-2123-ba4cf4128ac3@intel.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Sun, Apr 03, 2022, Zeng Guang wrote: > > On 4/1/2022 10:01 AM, Sean Christopherson wrote: > > Amusingly, I think we also need a capability to enumerate that KVM_CAP_MAX_VCPU_ID > > is writable. > > IIUC, KVM_CAP_*  has intrinsic writable attribute. KVM will return invalid > If not implemented. Yes, but forcing userspace to do a dummy write to detect support is rather ugly. I'm not totally opposed to it. Probably a Paolo question. Paolo? > > > + if (cap->args[0] <= KVM_MAX_VCPU_IDS) { > > > + kvm->arch.max_vcpu_id = cap->args[0]; > > This needs to be rejected if kvm->created_vcpus > 0, and that check needs to be > > done under kvm_lock, otherwise userspace can bump the max ID after KVM allocates > > per-VM structures and trigger buffer overflow. > > Is it necessary to use kvm_lock ? Seems no use case to call it from multi-threads. There's no sane use case, but userspace is untrusted, i.e. KVM can't assume that userspace will do the right/desired thing.