linux-kernel - Re: [PATCH v7 01/14] mm: Add F_SEAL_AUTO

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Message-ID: <20220810093859.GF862421@chaop.bj.intel.com>
Date:   Wed, 10 Aug 2022 17:38:59 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        linux-kselftest@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        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>,
        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>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "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>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
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        dhildenb@...hat.com, Quentin Perret <qperret@...gle.com>,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v7 01/14] mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd

On Fri, Aug 05, 2022 at 07:55:38PM +0200, Paolo Bonzini wrote:
> On 7/21/22 11:44, David Hildenbrand wrote:
> > 
> > Also, I*think*  you can place pages via userfaultfd into shmem. Not
> > sure if that would count "auto alloc", but it would certainly bypass
> > fallocate().
> 
> Yeah, userfaultfd_register would probably have to forbid this for
> F_SEAL_AUTO_ALLOCATE vmas.  Maybe the memfile_node can be reused for this,
> adding a new MEMFILE_F_NO_AUTO_ALLOCATE flags?  Then userfault_register
> would do something like memfile_node_get_flags(vma->vm_file) and check the
> result.

Then we need change userfault_register uAPI for a new property flag.
Userspace should still the decision-maker for this flag.

> 
> This means moving this patch later, after "mm: Introduce memfile_notifier".

Yes, it makes sense now.

Chao
> 
> Thanks,
> 
> Paolo