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From:   Fuad Tabba <tabba@google.com>
Date:   Thu, 27 Jul 2023 11:39:38 +0100
Message-ID: <CA+EHjTzP2fypgkJbRpSPrKaWytW7v8ANEifofMnQCkdvYaX6Eg@mail.gmail.com>
Subject: Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for
 guest-specific backing memory
To:     Sean Christopherson <seanjc@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, 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>,
        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>
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Hi Sean,

<snip>
...

> @@ -5134,6 +5167,16 @@ static long kvm_vm_ioctl(struct file *filp,
>         case KVM_GET_STATS_FD:
>                 r = kvm_vm_ioctl_get_stats_fd(kvm);
>                 break;
> +       case KVM_CREATE_GUEST_MEMFD: {
> +               struct kvm_create_guest_memfd guest_memfd;
> +
> +               r = -EFAULT;
> +               if (copy_from_user(&guest_memfd, argp, sizeof(guest_memfd)))
> +                       goto out;
> +
> +               r = kvm_gmem_create(kvm, &guest_memfd);
> +               break;
> +       }

I'm thinking line of sight here, by having this as a vm ioctl (rather
than a system iocl), would it complicate making it possible in the
future to share/donate memory between VMs?

Cheers,
/fuad