From: David Hildenbrand <david@redhat.com>
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>,
Hagen Paul Pfeifer <hagen@jauu.net>,
Ingo Molnar <mingo@redhat.com>,
James Bottomley <jejb@linux.ibm.com>,
Kees Cook <keescook@chromium.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Matthew Wilcox <willy@infradead.org>,
Matthew Garrett <mjg59@srcf.ucam.org>,
Mark Rutland <mark.rutland@arm.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Palmer Dabbelt <palmerdabbelt@google.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Peter Zijlstra <peterz@infradead.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
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>,
Yury Norov <yury.norov@gmail.com>,
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,
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x86@kernel.org
Subject: Re: [PATCH v19 5/8] mm: introduce memfd_secret system call to create "secret" memory areas
Date: Tue, 18 May 2021 12:35:36 +0200 [thread overview]
Message-ID: <00644dd8-edac-d3fd-a080-0a175fa9bf13@redhat.com> (raw)
In-Reply-To: <YKOXbNWvUsqM4uxb@dhcp22.suse.cz>
On 18.05.21 12:31, Michal Hocko wrote:
> On Tue 18-05-21 12:06:42, David Hildenbrand wrote:
>> On 18.05.21 11:59, Michal Hocko wrote:
>>> On Sun 16-05-21 10:29:24, Mike Rapoport wrote:
>>>> On Fri, May 14, 2021 at 11:25:43AM +0200, David Hildenbrand wrote:
>>> [...]
>>>>>> + if (!page)
>>>>>> + return VM_FAULT_OOM;
>>>>>> +
>>>>>> + err = set_direct_map_invalid_noflush(page, 1);
>>>>>> + if (err) {
>>>>>> + put_page(page);
>>>>>> + return vmf_error(err);
>>>>>
>>>>> Would we want to translate that to a proper VM_FAULT_..., which would most
>>>>> probably be VM_FAULT_OOM when we fail to allocate a pagetable?
>>>>
>>>> That's what vmf_error does, it translates -ESOMETHING to VM_FAULT_XYZ.
>>>
>>> I haven't read through the rest but this has just caught my attention.
>>> Is it really reasonable to trigger the oom killer when you cannot
>>> invalidate the direct mapping. From a quick look at the code it is quite
>>> unlikely to se ENOMEM from that path (it allocates small pages) but this
>>> can become quite sublte over time. Shouldn't this simply SIGBUS if it
>>> cannot manipulate the direct mapping regardless of the underlying reason
>>> for that?
>>>
>>
>> OTOH, it means our kernel zones are depleted, so we'd better reclaim somehow
>> ...
>
> Killing a userspace seems to be just a bad way around that.
>
> Although I have to say openly that I am not a great fan of VM_FAULT_OOM
> in general. It is usually a a wrong way to tell the handle the failure
> because it happens outside of the allocation context so you lose all the
> details (e.g. allocation constrains, numa policy etc.). Also whenever
> there is ENOMEM then the allocation itself has already made sure that
> all the reclaim attempts have been already depleted. Just consider an
> allocation with GFP_NOWAIT/NO_RETRY or similar to fail and propagate
> ENOMEM up the call stack. Turning that into the OOM killer sounds like a
> bad idea to me. But that is a more general topic. I have tried to bring
> this up in the past but there was not much of an interest to fix it as
> it was not a pressing problem...
>
I'm certainly interested; it would mean that we actually want to try
recovering from VM_FAULT_OOM in various cases, and as you state, we
might have to supply more information to make that work reliably.
Having that said, I guess what we have here is just the same as when our
process fails to allocate a generic page table in __handle_mm_fault(),
when we fail p4d_alloc() and friends ...
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-05-18 10:35 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-13 18:47 [PATCH v19 0/8] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-05-13 18:47 ` [PATCH v19 1/8] mmap: make mlock_future_check() global Mike Rapoport
2021-05-14 8:27 ` David Hildenbrand
2021-05-13 18:47 ` [PATCH v19 2/8] riscv/Kconfig: make direct map manipulation options depend on MMU Mike Rapoport
2021-05-14 8:28 ` David Hildenbrand
2021-05-13 18:47 ` [PATCH v19 3/8] set_memory: allow set_direct_map_*_noflush() for multiple pages Mike Rapoport
2021-05-14 8:43 ` David Hildenbrand
2021-05-16 7:13 ` Mike Rapoport
2021-05-13 18:47 ` [PATCH v19 4/8] set_memory: allow querying whether set_direct_map_*() is actually enabled Mike Rapoport
2021-05-13 18:47 ` [PATCH v19 5/8] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-05-14 8:50 ` David Hildenbrand
2021-05-17 7:23 ` Mike Rapoport
2021-05-14 9:25 ` David Hildenbrand
2021-05-16 7:29 ` Mike Rapoport
2021-05-18 9:59 ` Michal Hocko
2021-05-18 10:06 ` David Hildenbrand
2021-05-18 10:31 ` Michal Hocko
2021-05-18 10:35 ` David Hildenbrand [this message]
2021-05-18 11:08 ` Michal Hocko
2021-05-19 7:13 ` Mike Rapoport
2021-05-13 18:47 ` [PATCH v19 6/8] PM: hibernate: disable when there are active secretmem users Mike Rapoport
2021-05-14 9:27 ` David Hildenbrand
2021-05-18 10:24 ` Mark Rutland
2021-05-18 10:27 ` David Hildenbrand
2021-05-19 1:32 ` James Bottomley
2021-05-19 1:49 ` Dan Williams
2021-05-19 3:50 ` James Bottomley
2021-05-13 18:47 ` [PATCH v19 7/8] arch, mm: wire up memfd_secret system call where relevant Mike Rapoport
2021-05-14 9:27 ` David Hildenbrand
2021-05-13 18:47 ` [PATCH v19 8/8] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2021-05-14 9:40 ` David Hildenbrand
2021-05-13 19:08 ` [PATCH v19 0/8] mm: introduce memfd_secret system call to create "secret" memory areas James Bottomley
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