From: "Michael S. Tsirkin" <mst@redhat.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: KVM list <kvm@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
ghammer@redhat.com, "Weiss, Radu" <raduweis@amazon.com>,
Qemu Developers <qemu-devel@nongnu.org>,
"open list:VIRTIO GPU DRIVER"
<virtualization@lists.linux-foundation.org>,
Pavel Machek <pavel@ucw.cz>,
Colm MacCarthaigh <colmmacc@amazon.com>,
Jonathan Corbet <corbet@lwn.net>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Eric Biggers <ebiggers@kernel.org>,
"Singh, Balbir" <sblbir@amazon.com>,
bonzini@gnu.org, "Graf \(AWS\), Alexander" <graf@amazon.de>,
Jann Horn <jannh@google.com>,
oridgar@gmail.com, "Catangiu, Adrian Costin" <acatan@amazon.com>,
Andy Lutomirski <luto@kernel.org>,
Michal Hocko <mhocko@kernel.org>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
kernel list <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>, Willy Tarreau <w@1wt.eu>,
"Woodhouse, David" <dwmw@amazon.co.uk>
Subject: Re: [PATCH] drivers/virt: vmgenid: add vm generation id driver
Date: Sun, 18 Oct 2020 11:52:06 -0400 [thread overview]
Message-ID: <20201018114625-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CAHmME9qHGSF8w3DoyCP+ud_N0MAJ5_8zsUWx=rxQB1mFnGcu9w@mail.gmail.com>
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 ...
--
MST
next prev parent reply other threads:[~2020-10-18 15:53 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <AQHWo8lIfZnFKGe8nkGmhTCXwq5R3w==>
2020-10-16 14:33 ` [PATCH] drivers/virt: vmgenid: add vm generation id driver Catangiu, Adrian Costin
2020-10-16 15:00 ` Catangiu, Adrian Costin
2020-10-16 15:14 ` gregkh
2020-10-17 1:40 ` Jann Horn
2020-10-17 3:36 ` Willy Tarreau
2020-10-17 4:02 ` Jann Horn
2020-10-17 4:34 ` Colm MacCarthaigh
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 [this message]
2020-10-18 15:54 ` Andy Lutomirski
2020-10-18 15:59 ` Michael S. Tsirkin
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
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