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Peter Anvin" , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Subject: Re: [PATCH v6 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active To: Sean Christopherson , Borislav Petkov References: <1536343050-18532-1-git-send-email-brijesh.singh@amd.com> <1536343050-18532-6-git-send-email-brijesh.singh@amd.com> <20180910122727.GE21815@zn.tnic> <026d5ca5-7b77-de6c-477e-ff39f0291ac0@amd.com> <1536586152.11460.40.camel@intel.com> From: Brijesh Singh Message-ID: <097eb5f5-2cd9-8b08-32c5-d90c8e0cbb6d@amd.com> Date: Mon, 10 Sep 2018 10:10:09 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1536586152.11460.40.camel@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [165.204.77.1] X-ClientProxiedBy: SN6PR04CA0050.namprd04.prod.outlook.com (2603:10b6:805:2a::27) To DM6PR12MB2682.namprd12.prod.outlook.com (2603:10b6:5:4a::31) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 057cfb55-8cd5-4785-0772-08d6172f8240 X-MS-Office365-Filtering-HT: Tenant X-Microsoft-Antispam: BCL:0;PCL:0;RULEID:(7020095)(4652040)(8989137)(4534165)(4627221)(201703031133081)(201702281549075)(8990107)(5600074)(711020)(4618075)(2017052603328)(7153060)(7193020);SRVR:DM6PR12MB2682; 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>>> Hmm, so worst case that's 64 4K pages: >>> >>> (8192*32)/4096 = 64 4K pages. >> We can minimize the worst case memory usage. The number of VCPUs >> supported by KVM maybe less than NR_CPUS. e.g Currently KVM_MAX_VCPUS is >> set to 288 > > KVM_MAX_VCPUS is a property of the host, whereas this code runs in the > guest, e.g. KVM_MAX_VCPUS could be 2048 in the host for all we know. > IIRC, during guest creation time qemu will check the host supported VCPUS count. If count is greater than KVM_MAX_VCPUS then it will fail to launch guest (or fail to hot plug vcpus). In other words, the number of vcpus in a KVM guest will never to > KVM_MAX_VCPUS. Am I missing something ?