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[2003:d8:2f34:a300:1c2c:f35e:e8e5:488e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450d8000d8csm134568095e9.24.2025.06.02.13.13.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Jun 2025 13:13:15 -0700 (PDT) Message-ID: <42226b18-7cf5-41e4-8a0b-5b35ee50f119@redhat.com> Date: Mon, 2 Jun 2025 22:13:10 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] KVM: guest_memfd: Use guest mem inodes instead of anonymous inodes To: Ackerley Tng , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org Cc: aik@amd.com, ajones@ventanamicro.com, akpm@linux-foundation.org, amoorthy@google.com, anthony.yznaga@oracle.com, anup@brainfault.org, aou@eecs.berkeley.edu, bfoster@redhat.com, binbin.wu@linux.intel.com, brauner@kernel.org, catalin.marinas@arm.com, chao.p.peng@intel.com, chenhuacai@kernel.org, dave.hansen@intel.com, dmatlack@google.com, dwmw@amazon.co.uk, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, graf@amazon.com, haibo1.xu@intel.com, hch@infradead.org, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgg@ziepe.ca, jgowans@amazon.com, jhubbard@nvidia.com, jroedel@suse.de, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, kirill.shutemov@intel.com, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maz@kernel.org, mic@digikod.net, michael.roth@amd.com, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, pdurrant@amazon.co.uk, peterx@redhat.com, pgonda@google.com, pvorel@suse.cz, qperret@google.com, quic_cvanscha@quicinc.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, quic_svaddagi@quicinc.com, quic_tsoni@quicinc.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shuah@kernel.org, steven.price@arm.com, steven.sistare@oracle.com, suzuki.poulose@arm.com, tabba@google.com, thomas.lendacky@amd.com, vannapurve@google.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, wei.w.wang@intel.com, will@kernel.org, willy@infradead.org, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com, zhiquan1.li@intel.com References: <425cd410403e8913b42552d892add6ca543ec869.1748890962.git.ackerleytng@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 02.06.25 21:17, Ackerley Tng wrote: > guest_memfd's inode represents memory the guest_memfd is > providing. guest_memfd's file represents a struct kvm's view of that > memory. > > Using a custom inode allows customization of the inode teardown > process via callbacks. For example, ->evict_inode() allows > customization of the truncation process on file close, and > ->destroy_inode() and ->free_inode() allow customization of the inode > freeing process. > > Customizing the truncation process allows flexibility in management of > guest_memfd memory and customization of the inode freeing process > allows proper cleanup of memory metadata stored on the inode. > > Memory metadata is more appropriately stored on the inode (as opposed > to the file), since the metadata is for the memory and is not unique > to a specific binding and struct kvm. > > Signed-off-by: Ackerley Tng > Signed-off-by: Fuad Tabba The trailing SOB from Fuag is likely wrong. Probably you wnat Co-developed-by: Fuad Tabba Signed-off-by: Fuad Tabba Signed-off-by: Ackerley Tng > --- > include/uapi/linux/magic.h | 1 + > virt/kvm/guest_memfd.c | 134 +++++++++++++++++++++++++++++++------ > virt/kvm/kvm_main.c | 7 +- > virt/kvm/kvm_mm.h | 9 ++- > 4 files changed, 125 insertions(+), 26 deletions(-) > > diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h > index bb575f3ab45e..638ca21b7a90 100644 > --- a/include/uapi/linux/magic.h > +++ b/include/uapi/linux/magic.h > @@ -103,5 +103,6 @@ > #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */ > #define SECRETMEM_MAGIC 0x5345434d /* "SECM" */ > #define PID_FS_MAGIC 0x50494446 /* "PIDF" */ > +#define GUEST_MEMFD_MAGIC 0x474d454d /* "GMEM" */ > > #endif /* __LINUX_MAGIC_H__ */ > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index b2aa6bf24d3a..1283b85aeb44 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -1,12 +1,16 @@ > // SPDX-License-Identifier: GPL-2.0 > +#include > #include > #include > +#include > #include > +#include > #include > -#include > > #include "kvm_mm.h" > > +static struct vfsmount *kvm_gmem_mnt; > + > struct kvm_gmem { > struct kvm *kvm; > struct xarray bindings; > @@ -318,9 +322,51 @@ static struct file_operations kvm_gmem_fops = { > .fallocate = kvm_gmem_fallocate, > }; > > -void kvm_gmem_init(struct module *module) > +static const struct super_operations kvm_gmem_super_operations = { > + .statfs = simple_statfs, > +}; > + > +static int kvm_gmem_init_fs_context(struct fs_context *fc) > +{ > + struct pseudo_fs_context *ctx; > + > + if (!init_pseudo(fc, GUEST_MEMFD_MAGIC)) > + return -ENOMEM; > + > + ctx = fc->fs_private; > + ctx->ops = &kvm_gmem_super_operations; > + > + return 0; > +} > + > +static struct file_system_type kvm_gmem_fs = { > + .name = "kvm_guest_memory", > + .init_fs_context = kvm_gmem_init_fs_context, > + .kill_sb = kill_anon_super, > +}; > + > +static int kvm_gmem_init_mount(void) > +{ > + kvm_gmem_mnt = kern_mount(&kvm_gmem_fs); > + > + if (WARN_ON_ONCE(IS_ERR(kvm_gmem_mnt))) > + return PTR_ERR(kvm_gmem_mnt); Hmm, is this WARN_ON_ONCE really warrented? Nothing else jumped at me. I hope some fs experts can take a look as well. -- Cheers, David / dhildenb