From: "Michael S. Tsirkin" <mst@redhat.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
Jann Horn <jannh@google.com>, Willy Tarreau <w@1wt.eu>,
Colm MacCarthaigh <colmmacc@amazon.com>,
"Catangiu, Adrian Costin" <acatan@amazon.com>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
Eric Biggers <ebiggers@kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
kernel list <linux-kernel@vger.kernel.org>,
"open list:VIRTIO GPU DRIVER"
<virtualization@lists.linux-foundation.org>, "Graf (AWS),
Alexander" <graf@amazon.de>,
"Woodhouse, David" <dwmw@amazon.co.uk>,
bonzini@gnu.org, "Singh, Balbir" <sblbir@amazon.com>,
"Weiss, Radu" <raduweis@amazon.com>,
oridgar@gmail.com, ghammer@redhat.com,
Jonathan Corbet <corbet@lwn.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Qemu Developers <qemu-devel@nongnu.org>,
KVM list <kvm@vger.kernel.org>, Michal Hocko <mhocko@kernel.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Pavel Machek <pavel@ucw.cz>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH] drivers/virt: vmgenid: add vm generation id driver
Date: Sun, 18 Oct 2020 11:59:39 -0400 [thread overview]
Message-ID: <20201018115524-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CALCETrXBJZnKXo2QLKVWSgAhSMdwEVHeut6pRw4P92CR_5A-fQ@mail.gmail.com>
On Sun, Oct 18, 2020 at 08:54:36AM -0700, Andy Lutomirski wrote:
> On Sun, Oct 18, 2020 at 8:52 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Sat, Oct 17, 2020 at 03:24:08PM +0200, Jason A. Donenfeld wrote:
> > > 4c. The guest kernel maintains an array of physical addresses that are
> > > MADV_WIPEONFORK. The hypervisor knows about this array and its
> > > location through whatever protocol, and before resuming a
> > > moved/snapshotted/duplicated VM, it takes the responsibility for
> > > memzeroing this memory. The huge pro here would be that this
> > > eliminates all races, and reduces complexity quite a bit, because the
> > > hypervisor can perfectly synchronize its bringup (and SMP bringup)
> > > with this, and it can even optimize things like on-disk memory
> > > snapshots to simply not write out those pages to disk.
> > >
> > > A 4c-like approach seems like it'd be a lot of bang for the buck -- we
> > > reuse the existing mechanism (MADV_WIPEONFORK), so there's no new
> > > userspace API to deal with, and it'd be race free, and eliminate a lot
> > > of kernel complexity.
> >
> > Clearly this has a chance to break applications, right?
> > If there's an app that uses this as a non-system-calls way
> > to find out whether there was a fork, it will break
> > when wipe triggers without a fork ...
> > For example, imagine:
> >
> > MADV_WIPEONFORK
> > copy secret data to MADV_DONTFORK
> > fork
> >
> >
> > used to work, with this change it gets 0s instead of the secret data.
> >
> >
> > I am also not sure it's wise to expose each guest process
> > to the hypervisor like this. E.g. each process needs a
> > guest physical address of its own then. This is a finite resource.
> >
> >
> > The mmap interface proposed here is somewhat baroque, but it is
> > certainly simple to implement ...
>
> Wipe of fork/vmgenid/whatever could end up being much more problematic
> than it naively appears -- it could be wiped in the middle of a read.
> Either the API needs to handle this cleanly, or we need something more
> aggressive like signal-on-fork.
>
> --Andy
Right, it's not on fork, it's actually when process is snapshotted.
If we assume it's CRIU we care about, then I
wonder what's wrong with something like
MADV_CHANGEONPTRACE_SEIZE
and basically say it's X bytes which change the value...
--
MST
next prev parent reply other threads:[~2020-10-18 15:59 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <AQHWo8lIfZnFKGe8nkGmhTCXwq5R3w==>
[not found] ` <788878CE-2578-4991-A5A6-669DCABAC2F2@amazon.com>
2020-10-17 1:40 ` [PATCH] drivers/virt: vmgenid: add vm generation id driver Jann Horn
2020-10-17 3:36 ` Willy Tarreau
2020-10-17 4:02 ` Jann Horn
[not found] ` <6CC3DB03-27BA-4F5E-8ADA-BE605D83A85C@amazon.com>
2020-10-17 5:01 ` Jann Horn
2020-10-17 5:29 ` Colm MacCarthaigh
2020-10-17 5:37 ` Willy Tarreau
2020-10-17 5:52 ` Jann Horn
2020-10-17 6:44 ` Willy Tarreau
2020-10-17 6:55 ` Jann Horn
2020-10-17 7:17 ` Willy Tarreau
2020-10-17 13:24 ` Jason A. Donenfeld
2020-10-17 18:06 ` Catangiu, Adrian Costin
2020-10-17 18:09 ` Alexander Graf
2020-10-18 2:08 ` Jann Horn
2020-10-20 9:35 ` Christian Borntraeger
2020-10-20 9:54 ` Alexander Graf
2020-10-20 16:54 ` Catangiu, Adrian Costin
2020-10-18 3:14 ` Colm MacCarthaigh
2020-10-18 15:52 ` Michael S. Tsirkin
2020-10-18 15:54 ` Andy Lutomirski
2020-10-18 15:59 ` Michael S. Tsirkin [this message]
2020-10-18 16:14 ` Andy Lutomirski
2020-10-19 15:00 ` Michael S. Tsirkin
2020-10-17 18:10 ` Andy Lutomirski
2020-10-19 17:15 ` Mathieu Desnoyers
2020-10-20 10:00 ` Alexander Graf
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201018115524-mutt-send-email-mst@kernel.org \
--to=mst@redhat.com \
--cc=Jason@zx2c4.com \
--cc=acatan@amazon.com \
--cc=bonzini@gnu.org \
--cc=colmmacc@amazon.com \
--cc=corbet@lwn.net \
--cc=dwmw@amazon.co.uk \
--cc=ebiggers@kernel.org \
--cc=ghammer@redhat.com \
--cc=graf@amazon.de \
--cc=gregkh@linuxfoundation.org \
--cc=jannh@google.com \
--cc=kvm@vger.kernel.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mhocko@kernel.org \
--cc=oridgar@gmail.com \
--cc=pavel@ucw.cz \
--cc=qemu-devel@nongnu.org \
--cc=raduweis@amazon.com \
--cc=rafael@kernel.org \
--cc=sblbir@amazon.com \
--cc=tytso@mit.edu \
--cc=virtualization@lists.linux-foundation.org \
--cc=w@1wt.eu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).