linux-kernel - Re: [PATCH v9 8/9] KVM: x86: Allow userspace set maximum VCPU id for VM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <da1fc56f-bcfe-cc6e-aff7-0f95a3bc6d20@intel.com>
Date:   Tue, 3 May 2022 10:33:44 +0800
From:   Zeng Guang <guang.zeng@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Kim Phillips <kim.phillips@....com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        "Huang, Kai" <kai.huang@...el.com>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Hu, Robert" <robert.hu@...el.com>,
        "Gao, Chao" <chao.gao@...el.com>
Subject: Re: [PATCH v9 8/9] KVM: x86: Allow userspace set maximum VCPU id for
 VM


On 5/3/2022 12:07 AM, Paolo Bonzini wrote:
> On 4/19/22 17:44, Zeng Guang wrote:
>> +Userspace is able to calculate the limit to APIC ID values from designated CPU
>> +topology. This capability allows userspace to specify maximum possible APIC ID
>> +assigned for current VM session prior to the creation of vCPUs. By design, it
>> +can set only once and doesn't accept change any more. KVM will manage memory
>> +allocation of VM-scope structures which depends on the value of APIC ID.
>> +
>> +Calling KVM_CHECK_EXTENSION for this capability returns the value of maximum APIC
>> +ID that KVM supports at runtime. It sets as KVM_MAX_VCPU_IDS by default.
> Better:
>
> This capability allows userspace to specify maximum possible APIC ID
> assigned for current VM session prior to the creation of vCPUs, saving
> memory for data structures indexed by the APIC ID.  Userspace is able
> to calculate the limit to APIC ID values from designated
> CPU topology.
>
> The value can be changed only until KVM_ENABLE_CAP is set to a nonzero
> value or until a vCPU is created.  Upon creation of the first vCPU,
> if the value was set to zero or KVM_ENABLE_CAP was not invoked, KVM
> uses the return value of KVM_CHECK_EXTENSION(KVM_CAP_MAX_VCPU_ID) as
> the maximum APIC ID.
>
>>    	case KVM_CAP_MAX_VCPU_ID:
>> -		r = KVM_MAX_VCPU_IDS;
>> +		if (!kvm->arch.max_vcpu_ids)
>> +			r = KVM_MAX_VCPU_IDS;
>> +		else
>> +			r = kvm->arch.max_vcpu_ids;
> I think returning the constant KVM_CAP_MAX_VCPU_IDS is better.
>
> Paolo
Thanks. I will change as you suggested.