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AJvYcCX1YFfJStWs+hqLNJJCTBO7swQegnahnGFRNwuvl2NDapfSTD6nHcbyjJ22XUSn3v5GferWDq4Jgw==@kvack.org X-Gm-Message-State: AOJu0YzAwz5KbiqPcUYmb6fHudouvfNhUYR/ej4bN1vd6xMep1ZQOXGI +NusMGnj/WWl2Klfitw0bMPw0lqUHXl/HLJwV0OSE9idFkanqZJ5f/Vg4EzgcXQE7I92kPijaNe VoYcCemJBjT4pgTJ/iJ4OGS+Hi7gQPn0LdhBGpAUE X-Gm-Gg: ASbGnctrLUjPbCmy1qVTrZ6Cozvkb868oSXu8Ik/oLrhPtb8/XoH4v8ls55E/hlcA1f tdQ1glQzvSMJ3PmfzvSpwobUDPGCwFv/u8fw9UulHwh13UdoXFBJ4yWbfPuvNSRHTrQza4eguMM 28mugfrmp/+8MOVGrWohqgR1x3MOez9fe23ycqTcdJgdWDQa4kSUhjhu6yZWsaowXwL0asS7/r X-Google-Smtp-Source: AGHT+IG198J5XmfSPZMitL9d3FcAbULBcHuVy8v8Ee5QkIR46tmXRRtU6UF3dkNRuVzPV1IlHaErLL6ia9hlIQfVVi4= X-Received: by 2002:a17:902:e788:b0:216:4d90:47af with SMTP id d9443c01a7336-23c7ac47467mr572075ad.29.1751503973594; Wed, 02 Jul 2025 17:52:53 -0700 (PDT) MIME-Version: 1.0 References: <20250529054227.hh2f4jmyqf6igd3i@amd.com> <20250702232517.k2nqwggxfpfp3yym@amd.com> In-Reply-To: From: Vishal Annapurve Date: Wed, 2 Jul 2025 17:52:40 -0700 X-Gm-Features: Ac12FXxF97bn5vvTfJb7Vj8yqVTPgeruSo8qM9fM404AQ465bIDQRHsCOPgG6vA Message-ID: Subject: Re: [RFC PATCH v2 02/51] KVM: guest_memfd: Introduce and use shareability to guard faulting To: Michael Roth Cc: Ackerley Tng , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, aik@amd.com, ajones@ventanamicro.com, akpm@linux-foundation.org, amoorthy@google.com, anthony.yznaga@oracle.com, anup@brainfault.org, aou@eecs.berkeley.edu, bfoster@redhat.com, binbin.wu@linux.intel.com, brauner@kernel.org, catalin.marinas@arm.com, chao.p.peng@intel.com, chenhuacai@kernel.org, dave.hansen@intel.com, david@redhat.com, dmatlack@google.com, dwmw@amazon.co.uk, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, graf@amazon.com, haibo1.xu@intel.com, hch@infradead.org, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgg@ziepe.ca, jgowans@amazon.com, jhubbard@nvidia.com, jroedel@suse.de, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, kirill.shutemov@intel.com, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maz@kernel.org, mic@digikod.net, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, pdurrant@amazon.co.uk, peterx@redhat.com, pgonda@google.com, pvorel@suse.cz, qperret@google.com, quic_cvanscha@quicinc.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, quic_svaddagi@quicinc.com, quic_tsoni@quicinc.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shuah@kernel.org, steven.price@arm.com, steven.sistare@oracle.com, suzuki.poulose@arm.com, tabba@google.com, thomas.lendacky@amd.com, usama.arif@bytedance.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, wei.w.wang@intel.com, will@kernel.org, willy@infradead.org, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com, zhiquan1.li@intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 39E7D140006 X-Stat-Signature: 9jrkzac9gmbjairtg5gqyrkbn4ho1c7h X-HE-Tag: 1751503975-719426 X-HE-Meta: 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 bCqJCoqv Y0KZZWEabhFDGEhJd1sbLtF/d27GNJl8/rzI/Z78o79jTf+D+fl/XRwmv3qpHAcu9z4vAMeHViELLl4y33OEpSNVqFao1i2OaKZ9GCSzubNlZNqbzTRLZktDFicefDIksK82b67IBZ627SFIGwoxhUn6/sGGYZEA438TTKJRaVxGK388qfLeFGVXJLNCfbuXbjVA6Wi5QiFUSCqh8QJQo0quaMt1rWX8Yl6CifvE9sgu4jAqxNUG2vFNyXnN1Rbkb5KmGznVEphx6rLrZnoQH0O5h8OOuX7zuZh10TeqHy/Odwe8OblAGTlyhCrAzyjBtF2VnbFTxPAj71PuKMNn9t+04WA== 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 Wed, Jul 2, 2025 at 5:46=E2=80=AFPM Vishal Annapurve wrote: > ... > > > > 2) There are some use-cases for HugeTLB + CoCo that have come to my > > attention recently that put a lot of weight on still being able to > > maximize mapping/hugepage size when accessing shared mem from usersp= ace, > > e.g. for certain DPDK workloads that accessed shared guest buffers > > from host userspace. We don't really have a story for this, and I > > wouldn't expect us to at this stage, but I think it ties into #1 so > > might be worth considering in that context. > > Major problem I see here is that if anything in the kernel does a GUP > on shared memory ranges (which is very likely to happen), it would be > difficult to get them to let go of the whole hugepage before it can be > split safely. The scenario I was alluding to here: guest trying to convert a subpage from a shared range backed by hugepage to private.