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AJvYcCVzfj3+Y+MKq4a2GpFu3/FsjxOojU+SS3ZjNzxgJx0TS710vhDW5lEt7oP17AuWN2syJlM=@vger.kernel.org X-Gm-Message-State: AOJu0Yx+pdtzn66oNAdhpoKLJZJ2qQUko7h/gbtZhoV2i7QyBkFb9t2/ HhnNpnZrYpg7lzb1c2LfgkkNsaMN1YUv1MMtC4vyHzs8m0m3m1g1BowNfFOkI1j+eRRIoMWYEAi NrA== X-Google-Smtp-Source: AGHT+IHKJOwK2AYFShQ+asOEeUnEmwji9g2dnxKyKad6cMksYJ7+qH6/eE+gOCdEI6osazpQ8H6J0LE4s9o= X-Received: from pjb6.prod.google.com ([2002:a17:90b:2f06:b0:2ff:5752:a78f]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:dfc5:b0:2f4:4003:f3ea with SMTP id 98e67ed59e1d1-30a4e6addf7mr6247048a91.33.1746202920304; Fri, 02 May 2025 09:22:00 -0700 (PDT) Date: Fri, 2 May 2025 09:21:58 -0700 In-Reply-To: <386c1169-8292-43d1-846b-c50cbdc1bc65@redhat.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <386c1169-8292-43d1-846b-c50cbdc1bc65@redhat.com> Message-ID: Subject: Re: [PATCH v8 06/13] KVM: x86: Generalize private fault lookups to guest_memfd fault lookups From: Sean Christopherson To: David Hildenbrand Cc: Ackerley Tng , Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, mail@maciej.szmigiero.name, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com Content-Type: text/plain; charset="us-ascii" On Fri, May 02, 2025, David Hildenbrand wrote: > On 30.04.25 20:58, Ackerley Tng wrote: > > > - if (is_private) > > > + if (is_gmem) > > > return max_level; > > > > I think this renaming isn't quite accurate. > > After our discussion yesterday, does that still hold true? No. > > IIUC in __kvm_mmu_max_mapping_level(), we skip considering > > host_pfn_mapping_level() if the gfn is private because private memory > > will not be mapped to userspace, so there's no need to query userspace > > page tables in host_pfn_mapping_level(). > > I think the reason was that: for private we won't be walking the user space > pages tables. > > Once guest_memfd is also responsible for the shared part, why should this > here still be private-only, and why should we consider querying a user space > mapping that might not even exist? +1, one of the big selling points for guest_memfd beyond CoCo is that it provides guest-first memory. It is very explicitly an intended feature that the guest mappings KVM creates can be a superset of the host userspace mappings. E.g. the guest can use larger page sizes, have RW while the host has RO, etc.