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Message-ID: <e39a8f6e-c98d-4873-aa3f-2e566dead5c5@redhat.com>
Date:   Fri, 3 Nov 2023 11:40:56 +0100
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Subject: Re: [PATCH v13 15/35] fs: Export anon_inode_getfile_secure() for use
 by KVM
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To:     Christian Brauner <brauner@kernel.org>,
        Sean Christopherson <seanjc@google.com>
Cc:     Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Huacai Chen <chenhuacai@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Anup Patel <anup@brainfault.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Xiaoyao Li <xiaoyao.li@intel.com>,
        Xu Yilun <yilun.xu@intel.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Fuad Tabba <tabba@google.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Anish Moorthy <amoorthy@google.com>,
        David Matlack <dmatlack@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Isaku Yamahata <isaku.yamahata@intel.com>,
        =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= <mic@digikod.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
        David Hildenbrand <david@redhat.com>,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Wang <wei.w.wang@intel.com>,
        Liam Merwick <liam.merwick@oracle.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
References: <20231027182217.3615211-1-seanjc@google.com>
 <20231027182217.3615211-16-seanjc@google.com>
 <20231102-freihalten-vorsah-fdd68051b005@brauner>
From:   Paolo Bonzini <pbonzini@redhat.com>
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In-Reply-To: <20231102-freihalten-vorsah-fdd68051b005@brauner>
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On 11/2/23 17:24, Christian Brauner wrote:
> On Fri, Oct 27, 2023 at 11:21:57AM -0700, Sean Christopherson wrote:
>> Export anon_inode_getfile_secure() so that it can be used by KVM to create
>> and manage file-based guest memory without need a fullblow filesystem.
>> The "standard" anon_inode_getfd() doesn't work for KVM's use case as KVM
>> needs a unique inode for each file, e.g. to be able to independently
>> manage the size and lifecycle of a given file.
>>
>> Note, KVM doesn't need a "secure" version, just unique inodes, i.e. ignore
>> the name.
>>
>> Signed-off-by: Sean Christopherson <seanjc@google.com>
>> ---
> 
> Before we enshrine this misleading name let's rename this to:
> 
> create_anon_inode_getfile()
> 
> I don't claim it's a great name but it's better than *_secure() which is
> very confusing. So just:
> 
> struct file *create_anon_inode_getfile(const char *name,
>                                         const struct file_operations *fops,
>                                         void *priv, int flags)

I slightly prefer anon_inode_create_getfile(); grepping include/linux 
for '\<create_' vs '_create_' shows that this is much more common.

Neither userfaultfd (which uses anon_inode_getfd_secure()) nor io_uring 
strictly speaking need separate inodes; they do want the call to 
inode_init_security_anon().  But I agree that the new name is better and 
I will adjust the comments so that it is clear why you'd use this 
function instead of anon_inode_get{file,fd}().

> May also just remove that context_inode argument from the exported
> function. The only other caller is io_uring. And neither it nor this
> patchset need the context_inode thing afaict.

True, OTOH we might as well rename anon_inode_getfd_secure() to 
anon_inode_create_getfd(), and that one does need context_inode.

I'll Cc you on v14 and will carry the patch in my tree.

Paolo

> Merge conflict risk is
> extremely low so carrying that as part of this patchset is fine and
> shouldn't cause huge issues for you.
>