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AJvYcCXHkZoX8yamaXXlkz1fplyFo5s8cLGzbcKbsOWhmtSKrWhEDITAwXwYadIwIDGxgLkCNkAFmDpI2tqHTi1V@vger.kernel.org X-Gm-Message-State: AOJu0YzH2ab/fZnO/1HzQWZjJheSE3EfroU5SIQxT98YbrGa37+RnQkw rhpGq7zcopXP420ev42dj6N+DA1AGGQEiNOhdaClB1gaU8uso4lqi9lk2Ni8/CSABpbjUlXUj9N CbQbLmwm73rtoeqEmQ5RUQKRgbQ8kw3QLkRJnd79X X-Gm-Gg: ASbGnctZ/6jR0ujLw5WwTpur99HLGywO+ICNwmYRHGYzLjJM9qmjBZ/ibZXyvqXPvsr +UeKg6nXQLPk3B04fN69m0w0/XRW+bRSmykjTvwu2or42LYLJ4ksKxhABY4TaMDYZUDRjYY2mdl 9KuW8GNosUYPBMRPvsUglexCUJSAPDHVXYcx5I6loaiNuRh0Kqap2MpUm+ZIgFL2hc4yEBlrPX 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) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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.