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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id DA077C83F09 for ; Tue, 8 Jul 2025 22:55:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4423B6B0095; Tue, 8 Jul 2025 18:55:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3F2906B0096; Tue, 8 Jul 2025 18:55:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2BA4B6B0098; Tue, 8 Jul 2025 18:55:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 159046B0095 for ; Tue, 8 Jul 2025 18:55:07 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 98BBBB7AB1 for ; Tue, 8 Jul 2025 22:55:06 +0000 (UTC) X-FDA: 83642604612.24.7C3695B Received: from mail-pl1-f170.google.com (mail-pl1-f170.google.com [209.85.214.170]) by imf25.hostedemail.com (Postfix) with ESMTP id A83F1A0003 for ; Tue, 8 Jul 2025 22:55:04 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=IG1I7F0N; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf25.hostedemail.com: domain of vannapurve@google.com designates 209.85.214.170 as permitted sender) smtp.mailfrom=vannapurve@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1752015304; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=sVRWLCIynL9morDWnQADm8WuJ5jAoeJ4mXqExkRmYFA=; b=3fMKX6LKg4tiRmsL7RlRhMSc//u5Egw90pMxiu9Th/N+0kjoyQC8PeGrw34Wu4VIttAkID 99nZqBHpphb+v0fHFQcWpH5sznCzD5CBuHMl40ksYsMKHlBJ5iXRI+vftgK87Pw6p6Q/g5 4MzCE8R5KqKGdMKZwXMQAhiLMDunbMg= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1752015304; a=rsa-sha256; cv=none; b=ZbIJMe5GKBHwjIZgUv6i+0b/M7a3+LMT5MCrs8mLecNl1EItlYqB0b+7yYiQ7CNk1o8TjM W051EICZ+YcYRRLWoIwhK3bVYHQ0T1qnKqBqrMY0pLLDrH2yfsiqvUZ9mYA+i3w4VFgrUt 08LD14xn08IM5GabSBB/jJcQ3yWOVkg= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=IG1I7F0N; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf25.hostedemail.com: domain of vannapurve@google.com designates 209.85.214.170 as permitted sender) smtp.mailfrom=vannapurve@google.com Received: by mail-pl1-f170.google.com with SMTP id d9443c01a7336-2357c61cda7so33895ad.1 for ; Tue, 08 Jul 2025 15:55:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1752015303; x=1752620103; darn=kvack.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=sVRWLCIynL9morDWnQADm8WuJ5jAoeJ4mXqExkRmYFA=; b=IG1I7F0NFwj9ZzjBqQXyb6+4GoI2I5gdPo7FClk76iLhavdTZu68fg55BlGnQMrwBK zVh1hXbPSQunNyntLxxdpvFu3ut/U4NlnvvBQ9GjCWdKhxnFhARXs1knvaaZkFsEUcO+ msWvRCB1xtWHN54N2JhjbtLQQJCnVR13tMQJsyQ3hQpcrHdP5fX/3d98hGH4LY8ALYHL 8aorIaX20OLi0pcvrOka4RHYXEEeCP+4DjbagxxYaGuTCL8vflGuHsQqw49fIyl6P8Ar nFGLZVeQqLvPOUoJIUD8Yq2NHW9bVWUOC4ayyXmAvO6dkDRR5+nFVP+mcCzFnOx72ewU u31Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1752015303; x=1752620103; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=sVRWLCIynL9morDWnQADm8WuJ5jAoeJ4mXqExkRmYFA=; b=dUuHN6UeOguvIC7K0Gmd52gaXNBKPGUJ52lgL3Djn6beBxHyWSAmM9yf/5n4DERyH9 qj+iJOFm81bNSO1GmLtNLCFaOXr48pEv3uvHWYhkTnGLJP2S7OQdrpS5FSppg8qmPVVf 3fDMk8aEVcTgmwtnnYwjF0HExMYmQwCtBA0QbkSBm9FAUM7urRmGOgTJLofYSuQW18/2 dARgrwFN4JnTSN7tErFGxUcJp9Qjux+6hScnhzy9FqhdPK9r8JFbvHEwICWUVDy4jus5 KOpFUeBtObN4xjtXtWrTsjNcvkipUjBirErSaTZjerbC1qe7WQ9znwsStpU94PSpCwDr Hxzg== X-Forwarded-Encrypted: i=1; AJvYcCUkDDxLFMkQghnpT50iXvbvTZVVPLAKqzFwZM/4rmaeUvK1oTTHsPvE3JTEasXdvqLbAQs43mM9gw==@kvack.org X-Gm-Message-State: AOJu0YwLXFQiNb+6ELeInqnDBh22OwsIf9rw0BqsnXFGzRRAQXmzp38R LyFgTYtUomLdUfu9Uq5uVKhdBcF3NVn4m9R3ICAd75GRcM2CswJ64Uz1OLljeFIKWjdAYW9tPhj 3ITBkzG6d/RhKGL771qeS/t96AbirpoDmcVwex6AT X-Gm-Gg: ASbGncu0g16mQbydlPX2MidVlOnVkw9+UJvvZPhhQivjIgoy+Ir2Gw47U8oVA0M0p03 L2po3tZ6lT+9EYY50g86v77v9g/J4ALlSh7zaZ5gMf2XDiCThNIWkvdI6YCMJprAACk1RC5o5/n 8miBW5IB/J8CVk1Bg12eWNYgaAtOg/lfxs9gDfhKNcHN+2SrjCIIMfVRT6JleUK4f3bL+1EufnG rPULoJgl5BH X-Google-Smtp-Source: AGHT+IFppI8EWFIKjUXPtViP+KrA09dQbTHMiXzo/hVpg329+fXbE9z6q1NN0DYucfeQOt83ReE7/FOzhTi0IjwwLl4= X-Received: by 2002:a17:903:320d:b0:216:48d4:b3a8 with SMTP id d9443c01a7336-23dda3cf61dmr1101735ad.16.1752015303037; Tue, 08 Jul 2025 15:55:03 -0700 (PDT) MIME-Version: 1.0 References: <006899ccedf93f45082390460620753090c01914.camel@intel.com> In-Reply-To: From: Vishal Annapurve Date: Tue, 8 Jul 2025 15:54:49 -0700 X-Gm-Features: Ac12FXyERUa_xOAJgG7dIrmMf4kvAAP-pOIx0wDj5UJ0uC1eIt2Bz0JJ6_rlubA Message-ID: Subject: Re: [RFC PATCH v2 00/51] 1G page support for guest_memfd To: Sean Christopherson Cc: Rick P Edgecombe , "pvorel@suse.cz" , "kvm@vger.kernel.org" , "catalin.marinas@arm.com" , Jun Miao , "nsaenz@amazon.es" , Kirill Shutemov , "pdurrant@amazon.co.uk" , "peterx@redhat.com" , "x86@kernel.org" , "tabba@google.com" , "amoorthy@google.com" , "quic_svaddagi@quicinc.com" , "jack@suse.cz" , "vkuznets@redhat.com" , "quic_eberman@quicinc.com" , "keirf@google.com" , "mail@maciej.szmigiero.name" , "anthony.yznaga@oracle.com" , Wei W Wang , "palmer@dabbelt.com" , "Wieczor-Retman, Maciej" , Yan Y Zhao , "ajones@ventanamicro.com" , "willy@infradead.org" , "paul.walmsley@sifive.com" , Dave Hansen , "aik@amd.com" , "usama.arif@bytedance.com" , "quic_mnalajal@quicinc.com" , "fvdl@google.com" , "rppt@kernel.org" , "quic_cvanscha@quicinc.com" , "maz@kernel.org" , "vbabka@suse.cz" , "anup@brainfault.org" , "thomas.lendacky@amd.com" , "linux-kernel@vger.kernel.org" , "mic@digikod.net" , "oliver.upton@linux.dev" , Fan Du , "akpm@linux-foundation.org" , "steven.price@arm.com" , "muchun.song@linux.dev" , "binbin.wu@linux.intel.com" , Zhiquan1 Li , "rientjes@google.com" , "mpe@ellerman.id.au" , Erdem Aktas , "david@redhat.com" , "jgg@ziepe.ca" , "hughd@google.com" , "jhubbard@nvidia.com" , Haibo1 Xu , Isaku Yamahata , "jthoughton@google.com" , "steven.sistare@oracle.com" , "quic_pheragu@quicinc.com" , "jarkko@kernel.org" , "chenhuacai@kernel.org" , Kai Huang , "shuah@kernel.org" , "bfoster@redhat.com" , "dwmw@amazon.co.uk" , Chao P Peng , "pankaj.gupta@amd.com" , Alexander Graf , "nikunj@amd.com" , "viro@zeniv.linux.org.uk" , "pbonzini@redhat.com" , "yuzenghui@huawei.com" , "jroedel@suse.de" , "suzuki.poulose@arm.com" , "jgowans@amazon.com" , Yilun Xu , "liam.merwick@oracle.com" , "michael.roth@amd.com" , "quic_tsoni@quicinc.com" , Xiaoyao Li , "aou@eecs.berkeley.edu" , Ira Weiny , "richard.weiyang@gmail.com" , "kent.overstreet@linux.dev" , "qperret@google.com" , "dmatlack@google.com" , "james.morse@arm.com" , "brauner@kernel.org" , "roypat@amazon.co.uk" , "linux-fsdevel@vger.kernel.org" , "ackerleytng@google.com" , "pgonda@google.com" , "quic_pderrin@quicinc.com" , "hch@infradead.org" , "will@kernel.org" , "linux-mm@kvack.org" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: A83F1A0003 X-Stat-Signature: 8tukgixosg684bmnae96mjiasckarc7q X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1752015304-669012 X-HE-Meta: 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 ykscZMoM /rbbbEafhhT9HmT5U/f/bHXJCNWeY2NdmCpWIWGw44GfKzIrEEB+qRiMyLpzfXEddJp2dCGEFDnrFQRfWqE4ISWlZr+4gEz4YArYQnAB3TDyAl0s0U3MezeUBfAdGts2Hv/PTTkdwdDHfGXdgF3UfrgTDva8HXJRG8ugj1dTpKpwnuIajgLkuUy3Tb7jSyUXRt6oj1HweXp/6x/rEDfwmoRy4nDP41I07vXXApaRTklS/tjjL9hkscEsE9DjGok2j07QgN7lFOS7SZnjggTpOyjN6XTygIw+DY5te6y4rkDwU7VIO9OxokCZs/4LuaQC8M/HYD3W/HvGCmcy2kg4S0l5qlgGhTtxCqxEuBFGOOXJOtwlpKMdcK5sdSg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jul 8, 2025 at 12:59=E2=80=AFPM Sean Christopherson wrote: > > On Tue, Jul 08, 2025, Vishal Annapurve wrote: > > On Tue, Jul 8, 2025 at 11:03=E2=80=AFAM Sean Christopherson wrote: > > Few points that seem important here: > > 1) Userspace can and should be able to only dictate if memory contents > > need to be preserved on shared to private conversion. > > No, I was wrong, pKVM has use cases where it's desirable to preserve data= on > private =3D> shared conversions. > > Side topic, if you're going to use fancy indentation, align the indentati= on so > it's actually readable. > > > -> For SNP/TDX VMs: > > * Only usecase for preserving contents is initial memory > > population, which can be achieved by: > > - Userspace converting the ranges to shared, populating = the contents, > > converting them back to private and then calling SNP/T= DX specific > > existing ABI functions. > > * For runtime conversions, guest_memfd can't ensure memory conte= nts are > > preserved during shared to private conversions as the architec= tures > > don't support that behavior. > > * So IMO, this "preserve" flag doesn't make sense for SNP/TDX VM= s, even > > It makes sense, it's just not supported by the architecture *at runtime*.= Case > in point, *something* needs to allow preserving data prior to launching t= he VM. > If we want to go with the PRIVATE =3D> SHARED =3D> FILL =3D> PRIVATE appr= oach for TDX > and SNP, then we'll probably want to allow PRESERVE only until the VM ima= ge is > finalized. Maybe we can simplify the story a bit here for today, how about: 1) For shared to private conversions: * Is it safe to say that the conversion itself is always content preserving, it's upto the architecture what it does with memory contents on the private fa= ults? - During initial memory setup, userspace can control how private memory would be faulted in by architecture supported ABI operations. - After initial memory setup, userspace can't control how private memory would be faulted in. 2) For private to shared conversions: * Architecture decides what should be done with the memory on shared faults. - guest_memfd can query architecture whether to zero memory or not. -> guest_memfd will only take on the responsibility of zeroing if needed by the architecture on shared faults. -> Architecture is responsible for the behavior on private faults. In future, if there is a usecase for controlling runtime behavior of private faults, architecture can expose additional ABI that userspace can use after initiating guest_memfd conversion.