From: David Hildenbrand <david@redhat.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: 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>, Idan Yaniv <idan.yaniv@ibm.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>,
Thomas Gleixner <tglx@linutronix.de>,
Shuah Khan <shuah@kernel.org>, 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
Subject: Re: [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas
Date: Tue, 3 Nov 2020 11:11:51 +0100 [thread overview]
Message-ID: <5709dadf-81c6-5b40-93d4-fbef94d5aad8@redhat.com> (raw)
In-Reply-To: <20201103095247.GH4879@kernel.org>
On 03.11.20 10:52, Mike Rapoport wrote:
> On Mon, Nov 02, 2020 at 06:51:09PM +0100, David Hildenbrand wrote:
>>>> Assume you have a system with quite some ZONE_MOVABLE memory (esp. in
>>>> virtualized environments), eating up a significant amount of !ZONE_MOVABLE
>>>> memory dynamically at runtime can lead to non-obvious issues. It looks like
>>>> you have plenty of free memory, but the kernel might still OOM when trying
>>>> to do kernel allocations e.g., for pagetables. With CMA we at least know
>>>> what we're dealing with - it behaves like ZONE_MOVABLE except for the owner
>>>> that can place unmovable pages there. We can use it to compute statically
>>>> the amount of ZONE_MOVABLE memory we can have in the system without doing
>>>> harm to the system.
>>>
>>> Why would you say that secretmem allocates from !ZONE_MOVABLE?
>>> If we put boot time reservations aside, the memory allocation for
>>> secretmem follows the same rules as the memory allocations for any file
>>> descriptor. That means we allocate memory with GFP_HIGHUSER_MOVABLE.
>>
>> Oh, okay - I missed that! I had the impression that pages are unmovable and
>> allocating from ZONE_MOVABLE would be a violation of that?
>>
>>> After the allocation the memory indeed becomes unmovable but it's not
>>> like we are eating memory from other zones here.
>>
>> ... and here you have your problem. That's a no-no. We only allow it in very
>> special cases where it can't be avoided - e.g., vfio having to pin guest
>> memory when passing through memory to VMs.
>>
>> Hotplug memory, online it to ZONE_MOVABLE. Allocate secretmem. Try to unplug
>> the memory again -> endless loop in offline_pages().
>>
>> Or have a CMA area that gets used with GFP_HIGHUSER_MOVABLE. Allocate
>> secretmem. The owner of the area tries to allocate memory - always fails.
>> Purpose of CMA destroyed.
>>
>>>
>>>> Ideally, we would want to support page migration/compaction and allow for
>>>> allocation from ZONE_MOVABLE as well. Would involve temporarily mapping,
>>>> copying, unmapping. Sounds feasible, but not sure which roadblocks we would
>>>> find on the way.
>>>
>>> We can support migration/compaction with temporary mapping. The first
>>> roadblock I've hit there was that migration allocates 4K destination
>>> page and if we use it in secret map we are back to scrambling the direct
>>> map into 4K pieces. It still sounds feasible but not as trivial :)
>>
>> That sounds like the proper way for me to do it then.
>
> Although migration of secretmem pages sounds feasible now, there maybe
> other issues I didn't see because I'm not very familiar with
> migration/compaction code.
Migration of PMDs might also be feasible - and it would be even
cleaner. But I agree that that might require more work and starting with
something simpler (!movable) is the right way to move forward.
--
Thanks,
David / dhildenb
prev parent reply other threads:[~2020-11-03 10:12 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 13:28 [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-09-24 13:28 ` [PATCH v6 1/6] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 2/6] mmap: make mlock_future_check() global Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-09-29 4:58 ` Edgecombe, Rick P
2020-09-29 13:06 ` Mike Rapoport
2020-09-29 20:06 ` Edgecombe, Rick P
2020-09-30 10:35 ` Mike Rapoport
2020-09-30 20:11 ` Edgecombe, Rick P
2020-10-11 9:42 ` Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 4/6] arch, mm: wire up memfd_secret system call were relevant Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2020-09-25 7:41 ` Peter Zijlstra
2020-09-25 9:00 ` David Hildenbrand
2020-09-25 9:50 ` Peter Zijlstra
2020-09-25 10:31 ` Mark Rutland
2020-09-29 14:04 ` Mike Rapoport
2020-09-29 13:07 ` Mike Rapoport
2020-09-29 13:06 ` Mike Rapoport
2020-09-29 13:05 ` Mike Rapoport
2020-09-29 14:12 ` Peter Zijlstra
2020-09-29 14:31 ` Dave Hansen
2020-09-29 14:58 ` Mike Rapoport
2020-09-29 15:15 ` Peter Zijlstra
2020-09-30 10:27 ` Mike Rapoport
2020-09-30 14:39 ` James Bottomley
2020-09-30 14:45 ` David Hildenbrand
2020-09-30 15:17 ` James Bottomley
2020-09-30 15:25 ` David Hildenbrand
2020-09-30 15:09 ` Matthew Wilcox
2020-10-01 8:14 ` Mike Rapoport
2020-09-29 15:03 ` James Bottomley
2020-09-30 10:20 ` Mike Rapoport
2020-09-30 10:43 ` Peter Zijlstra
2020-09-24 13:29 ` [PATCH v6 6/6] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2020-09-24 13:35 ` [PATCH] man2: new page describing memfd_secret() system call Mike Rapoport
2020-09-24 14:55 ` Alejandro Colomar
2020-10-03 9:32 ` Alejandro Colomar
2020-10-05 7:32 ` Mike Rapoport
2020-11-16 21:01 ` [PATCH v2] memfd_secret.2: New " Alejandro Colomar
2020-11-17 6:26 ` Mike Rapoport
2020-09-25 2:34 ` [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas Andrew Morton
2020-09-25 6:42 ` Mike Rapoport
2020-11-01 11:09 ` Hagen Paul Pfeifer
2020-11-02 15:40 ` Mike Rapoport
2020-11-03 13:52 ` Hagen Paul Pfeifer
2020-11-03 16:30 ` Mike Rapoport
2020-11-04 11:39 ` Hagen Paul Pfeifer
2020-11-04 17:02 ` Mike Rapoport
2020-11-09 10:41 ` Hagen Paul Pfeifer
2020-11-02 9:11 ` David Hildenbrand
2020-11-02 9:31 ` David Hildenbrand
2020-11-02 17:43 ` Mike Rapoport
2020-11-02 17:51 ` David Hildenbrand
2020-11-03 9:52 ` Mike Rapoport
2020-11-03 10:11 ` David Hildenbrand [this message]
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