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[2003:cb:c706:2000:e44c:bc46:d8d3:be5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f258b44b2sm20103448f8f.20.2025.02.20.03.19.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Feb 2025 03:19:11 -0800 (PST) Message-ID: <54d1c436-0041-4e7b-a106-ab24a6643a56@redhat.com> Date: Thu, 20 Feb 2025 12:19:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 02/11] KVM: guest_memfd: Handle final folio_put() of guest_memfd pages To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org Cc: 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, vbabka@suse.cz, vannapurve@google.com, 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_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: <20250211121128.703390-1-tabba@google.com> <20250211121128.703390-3-tabba@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: cfm9jjr3z3b481xf84c19jjyxoc4unzt X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: BA493A000E X-Rspam-User: X-HE-Tag: 1740050357-920648 X-HE-Meta: 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 al1cOZ4z 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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 11.02.25 13:11, Fuad Tabba wrote: > Before transitioning a guest_memfd folio to unshared, thereby > disallowing access by the host and allowing the hypervisor to > transition its view of the guest page as private, we need to be > sure that the host doesn't have any references to the folio. > > This patch introduces a new type for guest_memfd folios, which > isn't activated in this series but is here as a placeholder and > to facilitate the code in the next patch. This will be used in > the future to register a callback that informs the guest_memfd > subsystem when the last reference is dropped, therefore knowing > that the host doesn't have any remaining references. > > Signed-off-by: Fuad Tabba > --- > include/linux/kvm_host.h | 9 +++++++++ > include/linux/page-flags.h | 17 +++++++++++++++++ > mm/debug.c | 1 + > mm/swap.c | 9 +++++++++ > virt/kvm/guest_memfd.c | 7 +++++++ > 5 files changed, 43 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index f34f4cfaa513..8b5f28f6efff 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -2571,4 +2571,13 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, > struct kvm_pre_fault_memory *range); > #endif > > +#ifdef CONFIG_KVM_GMEM_SHARED_MEM > +void kvm_gmem_handle_folio_put(struct folio *folio); > +#else > +static inline void kvm_gmem_handle_folio_put(struct folio *folio) > +{ > + WARN_ON_ONCE(1); > +} > +#endif > + > #endif > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 6dc2494bd002..734afda268ab 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -933,6 +933,17 @@ enum pagetype { > PGTY_slab = 0xf5, > PGTY_zsmalloc = 0xf6, > PGTY_unaccepted = 0xf7, > + /* > + * guestmem folios are used to back VM memory as managed by guest_memfd. > + * Once the last reference is put, instead of freeing these folios back > + * to the page allocator, they are returned to guest_memfd. > + * > + * For now, guestmem will only be set on these folios as long as they > + * cannot be mapped to user space ("private state"), with the plan of > + * always setting that type once typed folios can be mapped to user > + * space cleanly. > + */ I would move that comment above the CONFIG_KVM_GMEM_SHARED_MEM below. Similar to how we do it for (some of) the others. Acked-by: David Hildenbrand -- Cheers, David / dhildenb