Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <210c89b2-15a6-536d-b149-ea2d9f9fccda@amd.com>
Date:   Thu, 21 Jul 2022 23:36:05 +0200
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.10.0
Subject: Re: [PATCH v5 00/13] KVM: mm: fd-based approach for supporting KVM
 guest private memory
Content-Language: en-US
To:     Sean Christopherson <seanjc@google.com>
Cc:     Chao Peng <chao.p.peng@linux.intel.com>,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Andy Lutomirski <luto@kernel.org>,
        Steven Price <steven.price@arm.com>,
        kvm list <kvm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        Linux API <linux-api@vger.kernel.org>, qemu-devel@nongnu.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        the arch/x86 maintainers <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Hugh Dickins <hughd@google.com>,
        Jeff Layton <jlayton@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@kernel.org>,
        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "Nakajima, Jun" <jun.nakajima@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        David Hildenbrand <david@redhat.com>,
        Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
        nikunj@amd.com, ashish.kalra@amd.com
References: <83fd55f8-cd42-4588-9bf6-199cbce70f33@www.fastmail.com>
 <YksIQYdG41v3KWkr@google.com> <Ykslo2eo2eRXrpFR@google.com>
 <eefc3c74-acca-419c-8947-726ce2458446@www.fastmail.com>
 <Ykwbqv90C7+8K+Ao@google.com> <YkyEaYiL0BrDYcZv@google.com>
 <20220422105612.GB61987@chaop.bj.intel.com>
 <20220509223056.pyazfxjwjvipmytb@amd.com> <YnmjvX9ow4elYsY8@google.com>
 <c3ca63d6-db27-d783-40ca-486b3fbbced7@amd.com> <YtnCyqbI26QfRuOP@google.com>
From:   "Gupta, Pankaj" <pankaj.gupta@amd.com>
In-Reply-To: <YtnCyqbI26QfRuOP@google.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?bkZZM1FkMVFuVmxaaml6VHFRSUxtYUZReXVOeDg3NEd0NFd4b3NhQXZDL1dO?=
 =?utf-8?B?V2I2QTM5YjRQSDBoUEZkOC9XL3lDMEY0TmRheGNuMjNFUUsvV1A5YkRpSU1r?=
 =?utf-8?B?ci9WTFhwUENDYlFWRVdibDJpcWZXdXBMODNuVkV4MDNpYnl3TWp5Wkpkb1Fk?=
 =?utf-8?B?VlZoUGFKdG85MU1UWHJ3SThQQVUrZ3BpOFRYSkNDcUNRZFBJQU1YeWJMWk0v?=
 =?utf-8?B?eWtnUHRNTHU3U3dFaWdHbzRicFBWNkhLdXZNYWZ0U1FReVJ3VkJ2bExVTEJ3?=
 =?utf-8?B?cUpsY2RsRE03SDJjVFhYVmlyYkxBRkpwRXFNaWtlMCtURXJWdFdPOW8wOENk?=
 =?utf-8?B?dnZyUjYzSG11L1AycEkrNFBuamlHeXIwbW9xQ3VnU0tFcVU0OTAzQlhXeWNi?=
 =?utf-8?B?NkFKTyt6WHhkUlk3SnBDUndLdUFFWVdDTGpVN0pyd2NUVDROSHlaUXdoRXQy?=
 =?utf-8?B?MCs3U1FJTnRRV3dwU1dMSEZGQkVWaXNxZzRDNDU2amtFdklNbWE4M1lnREUz?=
 =?utf-8?B?aTdqaW9RY2t4dHNwSEk0T0ZFM0hVTjdZVWtuMlJxQk1mN0c1WFJIbnQ3OTll?=
 =?utf-8?B?UlVaM2g2UWM1WUFod2gwQnNSSXBDMy83a0ZBRmtyRGpZeXhwYmRHa2trV3Fi?=
 =?utf-8?B?eWY5bVNoVHJpbGx1V1hxV3dVcERwOWE2NmtRd1Z4cnJ4bzB5RUl6c2U3bHFW?=
 =?utf-8?B?V2w3cVZtbW1xTGNQTGtIekxIZGg1SnhIUlErM05WcHlVdEV4ZmRoWDE4aE9l?=
 =?utf-8?B?SlowSEFBQ2VtV0VaZVltOGxKcmVacExiWTJFRWtaY3ZSbUJ3ZkFPMmw3VUNC?=
 =?utf-8?B?d1FSWUcwRkJBNGhHN1NYa29KSFB1Q1k3NTFzLzY5dkxuTmVhMEJEWkxxUDl1?=
 =?utf-8?B?Kzg5YUsxMlhCUWZPV2tGeW5XbHdYSklUQzh1dEE5ekQ1NExCNElxYnhHVmU4?=
 =?utf-8?B?YnJ2K3NWR05tSFpnU05KUU1RaFBQT3BlWWxFQWoxem8rQ0VlOEVGYi9BVDVE?=
 =?utf-8?B?QWoyOE40V2orUkUvUVp5L2gxRm9qQlNLTkUxeHdZM24zYmhkOEN5Y00rSkU5?=
 =?utf-8?B?dEFoZThlaXA4eU5SRTBpSzh4aDRMVEZ0cm1FK3VNUS8waDU0VTViRWJOTUl6?=
 =?utf-8?B?ZjQ5L3c4SmtnVTRPeXNCV0VYcnkrZXVkYjNIdHVEUWZlSHJWS2c0aVptZUtH?=
 =?utf-8?B?MzJXUDRPYlVlSTJ3eldxWUtHSUl6TnYxV0psN1lIMkZkOXJXd3lYVThZRW5R?=
 =?utf-8?B?VUhpVzFpT1N5VndDVStMcmwrWFEzalZxNkU0RXpiR2tXNWlnR3Z5R0VRY0ZY?=
 =?utf-8?B?YUt1QXl2ZzhwbVc2Vk9zcWhIc0wreXZjNDlVWlpwdnJDc2pxL2xNSVFWYng2?=
 =?utf-8?B?bVJ2Q251WWcxU2R1bHBtdGVPRCs3ejg5Uk5KZHphaTE5ejhEbXFWL2hWZitI?=
 =?utf-8?B?ZWtEUmdwUEg1cGltNm9kc0RpQUVhdHozbzlVNUdDMHZiV2Z3SkhUMTg5Y2R0?=
 =?utf-8?B?cjNyR25EcFFYaTIvOU01OWVGbzdKK1lLVGlxOE95V25mT09OTk9JOW8yMFZB?=
 =?utf-8?B?TXExdkUxL2t3STVJZE4ydkYwTlZ6ajhLRlJCWm01dkVjN1BGUW5Nd3RvY01N?=
 =?utf-8?B?R1A5SEI0VEJCdGpsVlhubXlBTktOMFkxM3FvUFZXZVR5RmNVc1ZFWEhIUVRQ?=
 =?utf-8?B?NzVnKzlUeUpsOTEvTE82NDhLdVY5Zlh0dDZMUWhBYkhWTlFxTEFCLzc2OFgv?=
 =?utf-8?B?YnBjSlRQNDZ1WHZmSTNPODk5dFF1a1RiaktuVDNQZ2NXcFAxelcrdk00M1NO?=
 =?utf-8?B?cFVsaEJqZUtVUDRLQ0FYdENWZTdKYS9xeXJtRVFrZ0NyV2dZazRya2ZySWo3?=
 =?utf-8?B?ZXNvZ2p2OVVabE5HYUJ6V2s4RVBNVThUYTlLYlFLOXBwd0g5L1l6Mnk5RWVp?=
 =?utf-8?B?Q2VkZHNkUEJJWXQ3TWZqZlBLV2hjeTk1WXNIMEEvcktGTkVia1d6M0xkbVRk?=
 =?utf-8?B?aElpd1IxWENtMEdObUg3UlIxVjFucktib3hzRUY1UVArUG52NEU4dk43bHN6?=
 =?utf-8?B?VG5OQnRhRDFGQlJIVEtLbnNvUy92NVV0MklMQ3lYK09TVkkybUZqRE1hN1Jj?=
 =?utf-8?B?a0gzQklZK1FINnpEU1VVcjdub0NwRS82YWJEWVVicGt1ZGNtVVdnMlJCZElE?=
 =?utf-8?Q?qKmCm9CUGfeKVnDlbZzMHcU=3D?=
X-OriginatorOrg: amd.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 36ae7c10-47b5-486d-16d1-08da6b61097c
X-MS-Exchange-CrossTenant-AuthSource: CY4PR1201MB0181.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Jul 2022 21:36:14.4598
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: eLrCbP1RKq/ldTCiHzx4cnDQnyHqCz36UduLBdxvloASLGaW1F19/McYw69+SAyztSCIUuKSosgq9LrOSBrroQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR12MB3490
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,
        RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_PASS autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


>>>>>       * The current patch should just work, but prefer to have pre-boot guest
>>>>>         payload/firmware population into private memory for performance.
>>>>
>>>> Not just performance in the case of SEV, it's needed there because firmware
>>>> only supports in-place encryption of guest memory, there's no mechanism to
>>>> provide a separate buffer to load into guest memory at pre-boot time. I
>>>> think you're aware of this but wanted to point that out just in case.
>>>
>>> I view it as a performance problem because nothing stops KVM from copying from
>>> userspace into the private fd during the SEV ioctl().  What's missing is the
>>> ability for userspace to directly initialze the private fd, which may or may not
>>> avoid an extra memcpy() depending on how clever userspace is.
>> Can you please elaborate more what you see as a performance problem? And
>> possible ways to solve it?
> 
> Oh, I'm not saying there actually _is_ a performance problem.  What I'm saying is
> that in-place encryption is not a functional requirement, which means it's purely
> an optimization, and thus we should other bother supporting in-place encryption
> _if_ it would solve a performane bottleneck.

Understood. Thank you!

Best regards,
Pankaj