From: Mike Rapoport <rppt@kernel.org>
To: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@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>,
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Christopher Lameter <cl@linux.com>,
Dan Williams <dan.j.williams@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
David Hildenbrand <david@redhat.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>,
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Mark Rutland <mark.rutland@arm.com>,
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Shuah Khan <shuah@kernel.org>,
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Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
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linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org,
x86@kernel.org, Hagen Paul Pfeifer <hagen@jauu.net>,
Palmer Dabbelt <palmerdabbelt@google.com>
Subject: Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to create "secret" memory areas
Date: Thu, 11 Feb 2021 13:20:08 +0200 [thread overview]
Message-ID: <20210211112008.GH242749@kernel.org> (raw)
In-Reply-To: <YCTtSrCEvuBug2ap@dhcp22.suse.cz>
On Thu, Feb 11, 2021 at 09:39:38AM +0100, Michal Hocko wrote:
> On Thu 11-02-21 09:13:19, Mike Rapoport wrote:
> > On Tue, Feb 09, 2021 at 02:17:11PM +0100, Michal Hocko wrote:
> > > On Tue 09-02-21 11:09:38, Mike Rapoport wrote:
> [...]
> > > > Citing my older email:
> > > >
> > > > I've hesitated whether to continue to use new flags to memfd_create() or to
> > > > add a new system call and I've decided to use a new system call after I've
> > > > started to look into man pages update. There would have been two completely
> > > > independent descriptions and I think it would have been very confusing.
> > >
> > > Could you elaborate? Unmapping from the kernel address space can work
> > > both for sealed or hugetlb memfds, no? Those features are completely
> > > orthogonal AFAICS. With a dedicated syscall you will need to introduce
> > > this functionality on top if that is required. Have you considered that?
> > > I mean hugetlb pages are used to back guest memory very often. Is this
> > > something that will be a secret memory usecase?
> > >
> > > Please be really specific when giving arguments to back a new syscall
> > > decision.
> >
> > Isn't "syscalls have completely independent description" specific enough?
>
> No, it's not as you can see from questions I've had above. More on that
> below.
>
> > We are talking about API here, not the implementation details whether
> > secretmem supports large pages or not.
> >
> > The purpose of memfd_create() is to create a file-like access to memory.
> > The purpose of memfd_secret() is to create a way to access memory hidden
> > from the kernel.
> >
> > I don't think overloading memfd_create() with the secretmem flags because
> > they happen to return a file descriptor will be better for users, but
> > rather will be more confusing.
>
> This is quite a subjective conclusion. I could very well argue that it
> would be much better to have a single syscall to get a fd backed memory
> with spedific requirements (sealing, unmapping from the kernel address
> space).
> Neither of us would be clearly right or wrong.
100% agree :)
> A more important point is a future extensibility and usability, though.
> So let's just think of few usecases I have outlined above. Is it
> unrealistic to expect that secret memory should be sealable? What about
> hugetlb? Because if the answer is no then a new API is a clear win as the
> combination of flags would never work and then we would just suffer from
> the syscall multiplexing without much gain. On the other hand if
> combination of the functionality is to be expected then you will have to
> jam it into memfd_create and copy the interface likely causing more
> confusion. See what I mean?
I see your point, but I think that overloading memfd_create definitely gets
us into syscall multiplexing from day one and support for seals and huge
pages in the secretmem will not make it less of a multiplexer.
Sealing is anyway controlled via fcntl() and I don't think
MFD_ALLOW_SEALING makes much sense for the secretmem because it is there to
prevent rogue file sealing in tmpfs/hugetlbfs.
As for the huge pages, I'm not sure at all that supporting huge pages in
secretmem will involve hugetlbfs. And even if yes, adding SECRETMEM_HUGE
flag seems to me less confusing than saying "from kernel x.y you can use
MFD_CREATE | MFD_SECRET | MFD_HUGE" etc for all possible combinations.
> I by no means do not insist one way or the other but from what I have
> seen so far I have a feeling that the interface hasn't been thought
> through enough.
It has been, but we have different thoughts about it ;-)
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2021-02-11 11:20 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-08 8:49 [PATCH v17 00/10] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-02-08 8:49 ` [PATCH v17 01/10] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2021-02-08 8:49 ` [PATCH v17 02/10] mmap: make mlock_future_check() global Mike Rapoport
2021-02-08 8:49 ` [PATCH v17 03/10] riscv/Kconfig: make direct map manipulation options depend on MMU Mike Rapoport
2021-02-08 8:49 ` [PATCH v17 04/10] set_memory: allow set_direct_map_*_noflush() for multiple pages Mike Rapoport
2021-02-08 8:49 ` [PATCH v17 05/10] set_memory: allow querying whether set_direct_map_*() is actually enabled Mike Rapoport
2021-02-08 8:49 ` [PATCH v17 06/10] arm64: kfence: fix header inclusion Mike Rapoport
2021-02-08 8:49 ` [PATCH v17 07/10] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2021-02-08 10:49 ` Michal Hocko
2021-02-08 21:26 ` Mike Rapoport
2021-02-09 8:47 ` Michal Hocko
2021-02-09 9:09 ` Mike Rapoport
2021-02-09 13:17 ` Michal Hocko
2021-02-11 7:13 ` Mike Rapoport
2021-02-11 8:39 ` Michal Hocko
2021-02-11 9:01 ` David Hildenbrand
2021-02-11 9:38 ` Michal Hocko
2021-02-11 9:48 ` David Hildenbrand
2021-02-11 10:02 ` David Hildenbrand
2021-02-11 11:29 ` Mike Rapoport
2021-02-11 11:27 ` Mike Rapoport
2021-02-11 12:07 ` David Hildenbrand
2021-02-11 23:09 ` Mike Rapoport
2021-02-12 9:18 ` David Hildenbrand
2021-02-14 9:19 ` Mike Rapoport
2021-02-14 9:58 ` David Hildenbrand
2021-02-14 19:21 ` James Bottomley
2021-02-15 9:13 ` Michal Hocko
2021-02-15 18:14 ` James Bottomley
2021-02-15 19:20 ` Michal Hocko
2021-02-16 16:25 ` James Bottomley
2021-02-16 16:34 ` David Hildenbrand
2021-02-16 16:44 ` James Bottomley
2021-02-16 17:16 ` David Hildenbrand
2021-02-17 16:19 ` James Bottomley
2021-02-22 9:38 ` David Hildenbrand
2021-02-22 10:50 ` David Hildenbrand
2021-02-16 16:51 ` Michal Hocko
2021-02-11 11:20 ` Mike Rapoport [this message]
2021-02-11 12:30 ` Michal Hocko
2021-02-11 22:59 ` Mike Rapoport
2021-02-12 9:02 ` Michal Hocko
2021-02-08 8:49 ` [PATCH v17 08/10] PM: hibernate: disable when there are active secretmem users Mike Rapoport
2021-02-08 10:18 ` Michal Hocko
2021-02-08 10:32 ` David Hildenbrand
2021-02-08 10:51 ` Michal Hocko
2021-02-08 10:53 ` David Hildenbrand
2021-02-08 10:57 ` Michal Hocko
2021-02-08 11:13 ` David Hildenbrand
2021-02-08 11:14 ` David Hildenbrand
2021-02-08 11:26 ` David Hildenbrand
2021-02-08 12:17 ` Michal Hocko
2021-02-08 13:34 ` Michal Hocko
2021-02-08 13:40 ` David Hildenbrand
2021-02-08 21:28 ` Mike Rapoport
2021-02-22 7:34 ` Matthew Garrett
2021-02-22 10:23 ` Mike Rapoport
2021-02-22 18:27 ` Matthew Garrett
2021-02-22 19:17 ` Dan Williams
2021-02-22 19:21 ` James Bottomley
2021-02-08 8:49 ` [PATCH v17 09/10] arch, mm: wire up memfd_secret system call where relevant Mike Rapoport
2021-02-08 8:49 ` [PATCH v17 10/10] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2021-02-08 9:27 ` [PATCH v17 00/10] mm: introduce memfd_secret system call to create "secret" memory areas David Hildenbrand
2021-02-08 21:13 ` Mike Rapoport
2021-02-08 21:38 ` David Hildenbrand
2021-02-09 8:59 ` Michal Hocko
2021-02-09 9:15 ` David Hildenbrand
2021-02-09 9:53 ` Michal Hocko
2021-02-09 10:23 ` David Hildenbrand
2021-02-09 10:30 ` David Hildenbrand
2021-02-09 13:25 ` Michal Hocko
2021-02-09 16:17 ` David Hildenbrand
2021-02-09 20:08 ` Michal Hocko
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