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Thu, 23 Jan 2025 21:32:18 -0800 (PST) X-Google-Smtp-Source: AGHT+IHqtpZFSrhtF7huOze/hKmkOEqq4y/TfOMaysezICpsnQmSYkT3LOCtGnO0n3WPfw/BdJZyHQ== X-Received: by 2002:a05:6a20:244d:b0:1db:e464:7b69 with SMTP id adf61e73a8af0-1eb214e82damr43379243637.20.1737696737997; Thu, 23 Jan 2025 21:32:17 -0800 (PST) Received: from [192.168.68.55] ([180.233.125.64]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72f8a77c4ecsm909347b3a.121.2025.01.23.21.31.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jan 2025 21:32:17 -0800 (PST) Message-ID: <3e1780db-6e39-4508-8ce5-4d28771400e8@redhat.com> Date: Fri, 24 Jan 2025 15:31:56 +1000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v5 04/15] KVM: guest_memfd: Track mappability within a struct kvm_gmem_private 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, david@redhat.com, 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: <20250117163001.2326672-1-tabba@google.com> <20250117163001.2326672-5-tabba@google.com> From: Gavin Shan In-Reply-To: <20250117163001.2326672-5-tabba@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: hi0FIXQEOX_ihDmxHjnMTtBC5vXS_yknR9yhwLOEtWs_1737696739 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 460B2180009 X-Rspamd-Server: rspam10 X-Stat-Signature: bd7brorse1dt6e1eg5pcc9pbwesbhtsi X-HE-Tag: 1737696742-455122 X-HE-Meta: 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 Rbe1m/P6 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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: Hi Fuad, On 1/18/25 2:29 AM, Fuad Tabba wrote: > From: Ackerley Tng > > Track whether guest_memfd memory can be mapped within the inode, > since it is property of the guest_memfd's memory contents. > > The guest_memfd PRIVATE memory attribute is not used for two > reasons. First because it reflects the userspace expectation for > that memory location, and therefore can be toggled by userspace. > The second is, although each guest_memfd file has a 1:1 binding > with a KVM instance, the plan is to allow multiple files per > inode, e.g. to allow intra-host migration to a new KVM instance, > without destroying guest_memfd. > > Signed-off-by: Ackerley Tng > Co-developed-by: Vishal Annapurve > Signed-off-by: Vishal Annapurve > Co-developed-by: Fuad Tabba > Signed-off-by: Fuad Tabba > --- > virt/kvm/guest_memfd.c | 56 ++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 51 insertions(+), 5 deletions(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 6453658d2650..0a7b6cf8bd8f 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -18,6 +18,17 @@ struct kvm_gmem { > struct list_head entry; > }; > > +struct kvm_gmem_inode_private { > +#ifdef CONFIG_KVM_GMEM_MAPPABLE > + struct xarray mappable_offsets; > +#endif > +}; > + > +static struct kvm_gmem_inode_private *kvm_gmem_private(struct inode *inode) > +{ > + return inode->i_mapping->i_private_data; > +} > + > /** > * folio_file_pfn - like folio_file_page, but return a pfn. > * @folio: The folio which contains this index. > @@ -312,8 +323,28 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) > return gfn - slot->base_gfn + slot->gmem.pgoff; > } > > +static void kvm_gmem_evict_inode(struct inode *inode) > +{ > + struct kvm_gmem_inode_private *private = kvm_gmem_private(inode); > + > +#ifdef CONFIG_KVM_GMEM_MAPPABLE > + /* > + * .evict_inode can be called before private data is set up if there are > + * issues during inode creation. > + */ > + if (private) > + xa_destroy(&private->mappable_offsets); > +#endif > + > + truncate_inode_pages_final(inode->i_mapping); > + > + kfree(private); > + clear_inode(inode); > +} > + > static const struct super_operations kvm_gmem_super_operations = { > - .statfs = simple_statfs, > + .statfs = simple_statfs, > + .evict_inode = kvm_gmem_evict_inode, > }; > As I understood, ->destroy_inode() may be more suitable place where the xarray is released. ->evict_inode() usually detach the inode from the existing struct, to make it offline. ->destroy_inode() is actually the place where the associated resource (memory) is relased. Another benefit with ->destroy_inode() is we're not concerned to truncate_inode_pages_final() and clear_inode(). > static int kvm_gmem_init_fs_context(struct fs_context *fc) > @@ -440,6 +471,7 @@ static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, > loff_t size, u64 flags) > { > const struct qstr qname = QSTR_INIT(name, strlen(name)); > + struct kvm_gmem_inode_private *private; > struct inode *inode; > int err; > > @@ -448,10 +480,19 @@ static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, > return inode; > > err = security_inode_init_security_anon(inode, &qname, NULL); > - if (err) { > - iput(inode); > - return ERR_PTR(err); > - } > + if (err) > + goto out; > + > + err = -ENOMEM; > + private = kzalloc(sizeof(*private), GFP_KERNEL); > + if (!private) > + goto out; > + > +#ifdef CONFIG_KVM_GMEM_MAPPABLE > + xa_init(&private->mappable_offsets); > +#endif > + > + inode->i_mapping->i_private_data = private; > The whole block of code needs to be guarded by CONFIG_KVM_GMEM_MAPPABLE because kzalloc(sizeof(...)) is translated to kzalloc(0) when CONFIG_KVM_GMEM_MAPPABLE is disabled, and kzalloc() will always fail. It will lead to unusable guest-memfd if CONFIG_KVM_GMEM_MAPPABLE is disabled. > inode->i_private = (void *)(unsigned long)flags; > inode->i_op = &kvm_gmem_iops; > @@ -464,6 +505,11 @@ static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, > WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); > > return inode; > + > +out: > + iput(inode); > + > + return ERR_PTR(err); > } > > static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size, Thanks, Gavin