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Subject: Re: [PATCH v17 08/10] PM: hibernate: disable when there are active
 secretmem users
To:     Michal Hocko <mhocko@suse.com>
Cc:     Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christopher Lameter <cl@linux.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Elena Reshetova <elena.reshetova@intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        James Bottomley <jejb@linux.ibm.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Roman Gushchin <guro@fb.com>,
        Shakeel Butt <shakeelb@google.com>,
        Shuah Khan <shuah@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
        linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org,
        x86@kernel.org, Hagen Paul Pfeifer <hagen@jauu.net>,
        Palmer Dabbelt <palmerdabbelt@google.com>
References: <20210208084920.2884-1-rppt@kernel.org>
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 <38c0cad4-ac55-28e4-81c6-4e0414f0620a@redhat.com>
 <YCEXwUYepeQvEWTf@dhcp22.suse.cz>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <a488a0bb-def5-0249-99e2-4643787cef69@redhat.com>
Date:   Mon, 8 Feb 2021 11:53:58 +0100
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On 08.02.21 11:51, Michal Hocko wrote:
> On Mon 08-02-21 11:32:11, David Hildenbrand wrote:
>> On 08.02.21 11:18, Michal Hocko wrote:
>>> On Mon 08-02-21 10:49:18, Mike Rapoport wrote:
>>>> From: Mike Rapoport <rppt@linux.ibm.com>
>>>>
>>>> It is unsafe to allow saving of secretmem areas to the hibernation
>>>> snapshot as they would be visible after the resume and this essentially
>>>> will defeat the purpose of secret memory mappings.
>>>>
>>>> Prevent hibernation whenever there are active secret memory users.
>>>
>>> Does this feature need any special handling? As it is effectivelly
>>> unevictable memory then it should behave the same as other mlock, ramfs
>>> which should already disable hibernation as those cannot be swapped out,
>>> no?
>>>
>>
>> Why should unevictable memory not go to swap when hibernating? We're merely
>> dumping all of our system RAM (including any unmovable allocations) to swap
>> storage and the system is essentially completely halted.
>>
> My understanding is that mlock is never really made visible via swap
> storage.

"Using swap storage for hibernation" and "swapping at runtime" are two 
different things. I might be wrong, though.

-- 
Thanks,

David / dhildenb