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AJvYcCUEJUe9ZEyG7Jp7icAKvNVeKqc/8SepCDLlwJ608Fh5vnCDyGvZhASQXAtcSeUw0VImNuPzsQg1rbDScMkO@vger.kernel.org X-Gm-Message-State: AOJu0YxN+h3OhbX7+RpxDscqSlHaxSCi76w+yzev4V2LyfN2X27SDVXo 5SVfFFpdr3s3tw+JQd6Smket2++Ztnb7V7ySREJtWYi7FvPgzZ9jTESl00TgRL/NbsB2RaSVpv4 iiuqmG+iabbP+YksVyDoWpA== X-Google-Smtp-Source: AGHT+IEx90GrBY3H6MbzTcyDAQhZ2Ks2wua1pC+ws2C0H9wlTxI+92NL1aBLbDXxy63FmYi74R2O4wQAYik0gcC9+w== X-Received: from pjh15.prod.google.com ([2002:a17:90b:3f8f:b0:2fa:e9b:33b7]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:ea0a:b0:216:393b:23d4 with SMTP id d9443c01a7336-221a0ec9a77mr342976695ad.11.1740608960088; Wed, 26 Feb 2025 14:29:20 -0800 (PST) Date: Wed, 26 Feb 2025 22:29:19 +0000 In-Reply-To: (message from Fuad Tabba on Wed, 29 Jan 2025 10:15:23 +0000) Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Message-ID: Subject: Re: [RFC PATCH v5 04/15] KVM: guest_memfd: Track mappability within a struct kvm_gmem_private From: Ackerley Tng To: Fuad Tabba Cc: gshan@redhat.com, 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, vbabka@suse.cz, vannapurve@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 Content-Type: text/plain; charset="UTF-8" Fuad Tabba writes: > Hi Gavin, > > On Fri, 24 Jan 2025 at 05:32, Gavin Shan wrote: >> >> 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(). > > I see. I'll give this a try. > While working on 1G page support (old revision at [1]), I was looking at this. Using .destroy_inode to clean up private->mappable_offsets should work fine, and I agree this should be refactored to use .destroy_inode instead. Thanks for pointing this out! FWIW, for 1G page support, the truncation process has to be overridden to, so the .evict_inode override will have to come back. >> >> > 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. > > Good point, thanks for pointing this out. > > Cheers, > /fuad > >> > 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 >> [1] https://lore.kernel.org/all/cover.1726009989.git.ackerleytng@google.com/T/