Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize
 direct map fragmentation
To:     Michal Hocko <mhocko@suse.com>
Cc:     Mike Rapoport <rppt@kernel.org>,
        James Bottomley <jejb@linux.ibm.com>,
        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>,
        "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: <73738cda43236b5ac2714e228af362b67a712f5d.camel@linux.ibm.com>
 <YBPF8ETGBHUzxaZR@dhcp22.suse.cz>
 <6de6b9f9c2d28eecc494e7db6ffbedc262317e11.camel@linux.ibm.com>
 <YBkcyQsky2scjEcP@dhcp22.suse.cz> <20210202124857.GN242749@kernel.org>
 <6653288a-dd02-f9de-ef6a-e8d567d71d53@redhat.com>
 <YBlUXdwV93xMIff6@dhcp22.suse.cz>
 <211f0214-1868-a5be-9428-7acfc3b73993@redhat.com>
 <YBlgCl8MQuuII22w@dhcp22.suse.cz>
 <d4fe580a-ef0e-e13f-9ee4-16fb8b6d65dd@redhat.com>
 <YBlicIupOyPF9f3D@dhcp22.suse.cz>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <95625b83-f7e2-b27a-2b99-d231338047fb@redhat.com>
Date:   Tue, 2 Feb 2021 15:34:29 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.5.0
MIME-Version: 1.0
In-Reply-To: <YBlicIupOyPF9f3D@dhcp22.suse.cz>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 02.02.21 15:32, Michal Hocko wrote:
> On Tue 02-02-21 15:26:20, David Hildenbrand wrote:
>> On 02.02.21 15:22, Michal Hocko wrote:
>>> On Tue 02-02-21 15:12:21, David Hildenbrand wrote:
>>> [...]
>>>> I think secretmem behaves much more like longterm GUP right now
>>>> ("unmigratable", "lifetime controlled by user space", "cannot go on
>>>> CMA/ZONE_MOVABLE"). I'd either want to reasonably well control/limit it or
>>>> make it behave more like mlocked pages.
>>>
>>> I thought I have already asked but I must have forgotten. Is there any
>>> actual reason why the memory is not movable? Timing attacks?
>>
>> I think the reason is simple: no direct map, no copying of memory.
> 
> This is an implementation detail though and not something terribly hard
> to add on top later on. I was more worried there would be really
> fundamental reason why this is not possible. E.g. security implications.

I don't remember all the details. Let's see what Mike thinks regarding 
migration (e.g., security concerns).

-- 
Thanks,

David / dhildenb