linux-kernel - Re: [PATCH v5 00/13] KVM: mm: fd-based approach for supporting KVM guest private memory

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Message-ID: <ae7c9c7a-ecda-8c80-751f-f05dbc6489d7@redhat.com>
Date:   Fri, 22 Apr 2022 13:06:25 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Quentin Perret <qperret@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Steven Price <steven.price@....com>,
        kvm list <kvm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>, qemu-devel@...gnu.org,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v5 00/13] KVM: mm: fd-based approach for supporting KVM
 guest private memory

On 4/22/22 12:56, Chao Peng wrote:
>          /* memfile notifier flags */
>          #define MFN_F_USER_INACCESSIBLE   0x0001  /* memory allocated in the file is inaccessible from userspace (e.g. read/write/mmap) */
>          #define MFN_F_UNMOVABLE           0x0002  /* memory allocated in the file is unmovable */
>          #define MFN_F_UNRECLAIMABLE       0x0003  /* memory allocated in the file is unreclaimable (e.g. via kswapd or any other pathes) */

You probably mean BIT(0/1/2) here.

Paolo

>      When memfile_notifier is being registered, memfile_register_notifier will
>      need check these flags. E.g. for MFN_F_USER_INACCESSIBLE, it fails when
>      previous mmap-ed mapping exists on the fd (I'm still unclear on how to do
>      this). When multiple consumers are supported it also need check all
>      registered consumers to see if any conflict (e.g. all consumers should have
>      MFN_F_USER_INACCESSIBLE set). Only when the register succeeds, the fd is
>      converted into a private fd, before that, the fd is just a normal (shared)
>      one. During this conversion, the previous data is preserved so you can put
>      some initial data in guest pages (whether the architecture allows this is
>      architecture-specific and out of the scope of this patch).