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Date:   Tue, 8 Feb 2022 09:49:35 +0100
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To:     Vlastimil Babka <vbabka@suse.cz>,
        Chao Peng <chao.p.peng@linux.intel.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, qemu-devel@nongnu.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Hugh Dickins <hughd@google.com>,
        Jeff Layton <jlayton@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com,
        ak@linux.intel.com, Mike Rapoport <rppt@linux.ibm.com>
References: <20220118132121.31388-1-chao.p.peng@linux.intel.com>
 <20220118132121.31388-3-chao.p.peng@linux.intel.com>
 <25166513-3074-f3b9-12cc-420ba74f153e@suse.cz>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Subject: Re: [PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag
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On 07.02.22 19:51, Vlastimil Babka wrote:
> On 1/18/22 14:21, Chao Peng wrote:
>> Introduce a new memfd_create() flag indicating the content of the
>> created memfd is inaccessible from userspace. It does this by force
>> setting F_SEAL_INACCESSIBLE seal when the file is created. It also set
>> F_SEAL_SEAL to prevent future sealing, which means, it can not coexist
>> with MFD_ALLOW_SEALING.
>>
>> The pages backed by such memfd will be used as guest private memory in
>> confidential computing environments such as Intel TDX/AMD SEV. Since
>> page migration/swapping is not yet supported for such usages so these
>> pages are currently marked as UNMOVABLE and UNEVICTABLE which makes
>> them behave like long-term pinned pages.
> 
> Shouldn't the amount of such memory allocations be restricted? E.g. similar
> to secretmem_mmap() doing mlock_future_check().

I've raised this already in the past and Kirill wanted to look into it [1].

We'll most certainly need a way to limit/control the amount of
unswappable + unmovable ("worse than mlock" memory) a user/process can
consume via this mechanism.


[1]
https://lkml.kernel.org/r/20211122135933.arjxpl7wyskkwvwv@box.shutemov.name


-- 
Thanks,

David / dhildenb