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[2003:cb:c706:2000:e44c:bc46:d8d3:be5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f25a0fe5esm20657531f8f.99.2025.02.20.03.54.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Feb 2025 03:54:49 -0800 (PST) Message-ID: Date: Thu, 20 Feb 2025 12:54:46 +0100 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 02/10] 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, 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: <20250218172500.807733-1-tabba@google.com> <20250218172500.807733-3-tabba@google.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 18.02.25 18:24, 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 subsequent patch series. 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. > > This patch also introduces the configuration option, > KVM_GMEM_SHARED_MEM, which toggles support for mapping > guest_memfd shared memory at the host. > > Signed-off-by: Fuad Tabba > Acked-by: Vlastimil Babka > --- > include/linux/kvm_host.h | 4 ++++ > include/linux/page-flags.h | 17 +++++++++++++++++ > mm/debug.c | 1 + > mm/swap.c | 9 +++++++++ > virt/kvm/Kconfig | 5 +++++ > virt/kvm/guest_memfd.c | 7 +++++++ > 6 files changed, 43 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index f34f4cfaa513..3ad0719bfc4f 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -2571,4 +2571,8 @@ 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); > +#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. > + */ Same comment as to v3 regarding moving the comment. kvm_gmem_handle_folio_put() might be fixed with having it as an inline function for the time being as discussed. Acked-by: David Hildenbrand -- Cheers, David / dhildenb