Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 21 Jul 2023 10:50:06 -0700
In-Reply-To: <8ad7a846-64e9-a3f1-4bf1-731a994d62cb@redhat.com>
Mime-Version: 1.0
References: <20230718234512.1690985-1-seanjc@google.com> <20230718234512.1690985-13-seanjc@google.com>
 <8ad7a846-64e9-a3f1-4bf1-731a994d62cb@redhat.com>
Message-ID: <ZLrFTq2f1NXtlJWd@google.com>
Subject: Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for
 guest-specific backing memory
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.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>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Paul Moore <paul@paul-moore.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>, 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-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Fuad Tabba <tabba@google.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Vishal Annapurve <vannapurve@google.com>,
        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        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>
Content-Type: text/plain; charset="us-ascii"
Precedence: bulk

On Fri, Jul 21, 2023, Paolo Bonzini wrote:
> On 7/19/23 01:44, Sean Christopherson wrote:
> > +	inode = alloc_anon_inode(mnt->mnt_sb);
> > +	if (IS_ERR(inode))
> > +		return PTR_ERR(inode);
> > +
> > +	err = security_inode_init_security_anon(inode, &qname, NULL);
> > +	if (err)
> > +		goto err_inode;
> > +
> 
> I don't understand the need to have a separate filesystem.  If it is to
> fully setup the inode before it's given a struct file, why not just export
> anon_inode_make_secure_inode instead of security_inode_init_security_anon?

Ugh, this is why comments are important, I can't remember either.

I suspect I implemented a dedicated filesystem to kinda sorta show that we could
allow userspace to provide the mount point with e.g. NUMA hints[*].  But my
preference would be to not support a userspace provided mount and instead implement
fbind() to let userspace control NUMA and whatnot.

[*] https://lore.kernel.org/all/ef48935e5e6f947f6f0c6d748232b14ef5d5ad70.1681176340.git.ackerleytng@google.com