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From: Matthew Wilcox <willy@infradead.org>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Anthony Yznaga <anthony.yznaga@oracle.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	mhocko@kernel.org, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	viro@zeniv.linux.org.uk, akpm@linux-foundation.org,
	arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org,
	gerg@linux-m68k.org, ktkhai@virtuozzo.com, peterz@infradead.org,
	esyr@redhat.com, jgg@ziepe.ca, christian@kellner.me,
	areber@redhat.com, cyphar@cyphar.com, steven.sistare@oracle.com
Subject: Re: [RFC PATCH 0/5] madvise MADV_DOEXEC
Date: Thu, 30 Jul 2020 16:34:50 +0100
Message-ID: <20200730153450.GH23808@casper.infradead.org> (raw)
In-Reply-To: <20200730152705.ol42jppnl4xfhl32@wittgenstein>

On Thu, Jul 30, 2020 at 05:27:05PM +0200, Christian Brauner wrote:
> On Thu, Jul 30, 2020 at 04:22:50PM +0100, Matthew Wilcox wrote:
> > On Mon, Jul 27, 2020 at 10:11:22AM -0700, Anthony Yznaga wrote:
> > > This patchset adds support for preserving an anonymous memory range across
> > > exec(3) using a new madvise MADV_DOEXEC argument.  The primary benefit for
> > > sharing memory in this manner, as opposed to re-attaching to a named shared
> > > memory segment, is to ensure it is mapped at the same virtual address in
> > > the new process as it was in the old one.  An intended use for this is to
> > > preserve guest memory for guests using vfio while qemu exec's an updated
> > > version of itself.  By ensuring the memory is preserved at a fixed address,
> > > vfio mappings and their associated kernel data structures can remain valid.
> > > In addition, for the qemu use case, qemu instances that back guest RAM with
> > > anonymous memory can be updated.
> > 
> > I just realised that something else I'm working on might be a suitable
> > alternative to this.  Apologies for not realising it sooner.
> > 
> > http://www.wil.cx/~willy/linux/sileby.html
> 
> Just skimming: make it O_CLOEXEC by default. ;)

I appreciate the suggestion, and it makes sense for many 'return an fd'
interfaces, but the point of mshare() is to, well, share.  So sharing
the fd with a child is a common usecase, unlike say sharing a timerfd.
The only other reason to use mshare() is to pass the fd over a unix
socket to a non-child, and I submit that is far less common than wanting
to share with a child.



  reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-27 17:11 Anthony Yznaga
2020-07-27 17:07 ` Eric W. Biederman
2020-07-27 18:00   ` Steven Sistare
2020-07-28 13:40     ` Christian Brauner
2020-07-27 17:11 ` [RFC PATCH 1/5] elf: reintroduce using MAP_FIXED_NOREPLACE for elf executable mappings Anthony Yznaga
2020-07-27 17:11 ` [RFC PATCH 2/5] mm: do not assume only the stack vma exists in setup_arg_pages() Anthony Yznaga
2020-07-27 17:11 ` [RFC PATCH 3/5] mm: introduce VM_EXEC_KEEP Anthony Yznaga
2020-07-28 13:38   ` Eric W. Biederman
2020-07-28 17:44     ` Anthony Yznaga
2020-07-29 13:52   ` Kirill A. Shutemov
2020-07-29 23:20     ` Anthony Yznaga
2020-07-27 17:11 ` [RFC PATCH 4/5] exec, elf: require opt-in for accepting preserved mem Anthony Yznaga
2020-07-27 17:11 ` [RFC PATCH 5/5] mm: introduce MADV_DOEXEC Anthony Yznaga
2020-07-28 13:22   ` Kirill Tkhai
2020-07-28 14:06     ` Steven Sistare
2020-07-28 11:34 ` [RFC PATCH 0/5] madvise MADV_DOEXEC Kirill Tkhai
2020-07-28 17:28   ` Anthony Yznaga
2020-07-28 14:23 ` Andy Lutomirski
2020-07-28 14:30   ` Steven Sistare
2020-07-30 15:22 ` Matthew Wilcox
2020-07-30 15:27   ` Christian Brauner
2020-07-30 15:34     ` Matthew Wilcox [this message]
2020-07-30 15:54       ` Christian Brauner
2020-07-31  9:12     ` Stefan Hajnoczi
2020-07-30 15:59   ` Steven Sistare
2020-07-30 17:12     ` Matthew Wilcox
2020-07-30 17:35       ` Steven Sistare
2020-07-30 17:49         ` Matthew Wilcox
2020-07-30 18:27           ` Steven Sistare
2020-07-30 21:58             ` Eric W. Biederman
2020-07-31 14:57               ` Steven Sistare
2020-07-31 15:27                 ` Matthew Wilcox
2020-07-31 16:11                   ` Steven Sistare
2020-07-31 16:56                     ` Jason Gunthorpe
2020-07-31 17:15                       ` Steven Sistare
2020-07-31 17:48                         ` Jason Gunthorpe
2020-07-31 17:55                           ` Steven Sistare
2020-07-31 17:23                     ` Matthew Wilcox
2020-08-03 15:28                 ` Eric W. Biederman
2020-08-03 15:42                   ` James Bottomley
2020-08-03 20:03                     ` Steven Sistare
     [not found]                     ` <9371b8272fd84280ae40b409b260bab3@AcuMS.aculab.com>
2020-08-04 11:13                       ` Matthew Wilcox
2020-08-03 19:29                   ` Steven Sistare
2020-07-31 19:41 ` Steven Sistare

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