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[2003:cb:c714:3600:8033:4189:6bd4:ea29]) by smtp.gmail.com with ESMTPSA id bx6-20020a5d5b06000000b00341e67a7a90sm1581093wrb.19.2024.03.28.04.41.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Mar 2024 04:41:37 -0700 (PDT) Message-ID: <3448a9d6-58a8-475f-aff6-a39a62eee8c1@redhat.com> Date: Thu, 28 Mar 2024 12:41:35 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: folio_mmapped To: Quentin Perret Cc: Will Deacon , Sean Christopherson , Vishal Annapurve , Matthew Wilcox , Fuad Tabba , kvm@vger.kernel.org, kvmarm@lists.linux.dev, 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, 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, yu.c.zhang@linux.intel.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, ackerleytng@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_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, keirf@google.com, linux-mm@kvack.org References: <7470390a-5a97-475d-aaad-0f6dfb3d26ea@redhat.com> <40f82a61-39b0-4dda-ac32-a7b5da2a31e8@redhat.com> <20240319143119.GA2736@willie-the-truck> <2d6fc3c0-a55b-4316-90b8-deabb065d007@redhat.com> <20240327193454.GB11880@willie-the-truck> <5cec1f98-17a5-4120-bbf4-b487c2caf92c@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: EE3221C0015 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: k7166cr5sn4h5woior3oewyeo5ygyk1a X-HE-Tag: 1711626101-331636 X-HE-Meta: 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 5pgxch9B 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 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 28.03.24 11:58, Quentin Perret wrote: > On Thursday 28 Mar 2024 at 11:32:21 (+0100), David Hildenbrand wrote: >> ... does that mean that for pKVM with protected VMs, "shared" pages are also >> never migratable/swappable? > > In our current implementation, yes, KVM keeps its longterm GUP pin on > pages that are shared back. And we might want to retain this behaviour > in the short term, even with guest_memfd or using the hybrid approach > you suggested. But that could totally be relaxed in the future, it's > "just" a matter of adding extra support to the hypervisor for that. That > has not been prioritized yet since the number of shared pages in > practice is relatively small for current use-cases, so ballooning was a > better option (and in the case of ballooning, we do drop the GUP pin). > But that's clearly on the TODO list! Okay, so nothing "fundamental", good! > >> The whole reason I brought up the guest_memfd+memfd pair idea is that you >> would similarly be able to do the conversion in the kernel, BUT, you'd never >> be able to mmap+GUP encrypted pages. >> >> Essentially you're using guest_memfd for what it was designed for: private >> memory that is inaccessible. > > Ack, that sounds pretty reasonable to me. But I think we'd still want to > make sure the other users of guest_memfd have the _desire_ to support > huge pages, migration, swap (probably longer term), and related > features, otherwise I don't think a guest_memfd-based option will > really work for us :-) *Probably* some easy way to get hugetlb pages into a guest_memfd would be by allocating them for an memfd and then converting/moving them into the guest_memfd part of the "fd pair" on conversion to private :) (but the "partial shared, partial private" case is and remains the ugly thing that is hard and I still don't think it makes sense. Maybe it could be handles somehow in such a dual approach with some enlightment in the fds ... hard to find solutions for things that don't make any sense :P ) I also do strongly believe that we want to see some HW-assisted migration support for guest_memfd pages. Swap, as you say, maybe in the long-term. After all, we're not interested in having MM features for backing memory that you could similarly find under Windows 95. Wait, that one did support swapping! :P But unfortunately, that's what the shiny new CoCo world currently offers. Well, excluding s390x secure execution, as discussed. -- Cheers, David / dhildenb