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[2003:d8:2f22:1000:d72d:fd5f:4118:c70b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38bf327df79sm10028340f8f.91.2025.01.20.01.36.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jan 2025 01:36:44 -0800 (PST) Message-ID: Date: Mon, 20 Jan 2025 10:36:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v4 00/14] KVM: Restricted mapping of guest_memfd at the host and arm64 support To: Vlastimil Babka , Fuad Tabba , Ackerley Tng Cc: 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, seanjc@google.com, 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, yu.c.zhang@linux.intel.com, isaku.yamahata@intel.com, mic@digikod.net, 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 References: From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 7CE07C0017 X-Stat-Signature: ywopor9frtb7m3mxicg6f5w9t74riqe1 X-HE-Tag: 1737365809-27966 X-HE-Meta: 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 UxGJlcA1 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000008, 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 20.01.25 10:26, Vlastimil Babka wrote: > On 1/16/25 10:19, Fuad Tabba wrote: >> Hi Ackerley, >> >> On Thu, 16 Jan 2025 at 00:35, Ackerley Tng wrote: >>> >>> Registration of the folio_put() callback only happens if the VMM >>> actually tries to do vcpu_run(). For 4K folios I think this is okay >>> since the 4K folio can be freed via the transition state K -> state I, >>> but for hugetlb folios that have been split for sharing with userspace, >>> not getting a folio_put() callback means never putting the hugetlb folio >>> together. Hence, relying on vcpu_run() to add the folio_put() callback >>> leaves a way that hugetlb pages can be removed from the system. >>> >>> I think we should try and find a path forward that works for both 4K and >>> hugetlb folios. >> >> I agree, this could be an issue, but we could find other ways to >> trigger the callback for huge folios. The important thing I was trying >> to get to is how to have the callback and be able to register it. >> >>> IIUC page._mapcount and page.page_type works as a union because >>> page_type is only set for page types that are never mapped to userspace, >>> like PGTY_slab, PGTY_offline, etc. >> >> In the last guest_memfd sync, David Hildenbrand mentioned that that >> would be a temporary restriction since the two structures would >> eventually be decoupled, work being done by Matthew Wilcox I believe. > > Note the "temporary" might be few years still, it's a long-term project. Right, nobody knows how long it will actually take. Willy thinks the part that would be required here might be feasible in the nearer future: "'d like to lay out some goals for the coming year. I think we can accomplish a big goal this year" [1] [1] https://lore.kernel.org/all/Z37pxbkHPbLYnDKn@casper.infradead.org/T/#u -- Cheers, David / dhildenb