From: Mike Rapoport <rppt@linux.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
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>,
David Hildenbrand <david@redhat.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>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
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 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation
Date: Tue, 29 Sep 2020 17:58:13 +0300 [thread overview]
Message-ID: <20200929145813.GA3226834@linux.ibm.com> (raw)
In-Reply-To: <20200929141216.GO2628@hirez.programming.kicks-ass.net>
On Tue, Sep 29, 2020 at 04:12:16PM +0200, Peter Zijlstra wrote:
> On Tue, Sep 29, 2020 at 04:05:29PM +0300, Mike Rapoport wrote:
> > On Fri, Sep 25, 2020 at 09:41:25AM +0200, Peter Zijlstra wrote:
> > > On Thu, Sep 24, 2020 at 04:29:03PM +0300, Mike Rapoport wrote:
> > > > From: Mike Rapoport <rppt@linux.ibm.com>
> > > >
> > > > Removing a PAGE_SIZE page from the direct map every time such page is
> > > > allocated for a secret memory mapping will cause severe fragmentation of
> > > > the direct map. This fragmentation can be reduced by using PMD-size pages
> > > > as a pool for small pages for secret memory mappings.
> > > >
> > > > Add a gen_pool per secretmem inode and lazily populate this pool with
> > > > PMD-size pages.
> > >
> > > What's the actual efficacy of this? Since the pmd is per inode, all I
> > > need is a lot of inodes and we're in business to destroy the directmap,
> > > no?
> > >
> > > Afaict there's no privs needed to use this, all a process needs is to
> > > stay below the mlock limit, so a 'fork-bomb' that maps a single secret
> > > page will utterly destroy the direct map.
> >
> > This indeed will cause 1G pages in the direct map to be split into 2M
> > chunks, but I disagree with 'destroy' term here. Citing the cover letter
> > of an earlier version of this series:
>
> It will drop them down to 4k pages. Given enough inodes, and allocating
> only a single sekrit page per pmd, we'll shatter the directmap into 4k.
Why? Secretmem allocates PMD-size page per inode and uses it as a pool
of 4K pages for that inode. This way it ensures that
__kernel_map_pages() is always called on PMD boundaries.
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2020-09-29 14:59 UTC|newest]
Thread overview: 57+ 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
2020-09-25 14:57 ` Tycho Andersen
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 [this message]
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
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