linux-kernel - RE: [RFC PATCH 0/5] madvise MADV

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Date:   Tue, 4 Aug 2020 08:44:42 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'James Bottomley' <James.Bottomley@...senPartnership.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Steven Sistare <steven.sistare@...cle.com>
CC:     Matthew Wilcox <willy@...radead.org>,
        Anthony Yznaga <anthony.yznaga@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
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        "keescook@...omium.org" <keescook@...omium.org>,
        "gerg@...ux-m68k.org" <gerg@...ux-m68k.org>,
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        "christian.brauner@...ntu.com" <christian.brauner@...ntu.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "esyr@...hat.com" <esyr@...hat.com>, "jgg@...pe.ca" <jgg@...pe.ca>,
        "christian@...lner.me" <christian@...lner.me>,
        "areber@...hat.com" <areber@...hat.com>,
        "cyphar@...har.com" <cyphar@...har.com>
Subject: RE: [RFC PATCH 0/5] madvise MADV_DOEXEC

From: James Bottomley
> Sent: 03 August 2020 16:43
> 
> On Mon, 2020-08-03 at 10:28 -0500, Eric W. Biederman wrote:
> [...]
> > What is wrong with live migration between one qemu process and
> > another qemu process on the same machine not work for this use case?
> >
> > Just reusing live migration would seem to be the simplest path of
> > all, as the code is already implemented.  Further if something goes
> > wrong with the live migration you can fallback to the existing
> > process.  With exec there is no fallback if the new version does not
> > properly support the handoff protocol of the old version.
> 
> Actually, could I ask this another way: the other patch set you sent to
> the KVM list was to snapshot the VM to a PKRAM capsule preserved across
> kexec using zero copy for extremely fast save/restore.  The original
> idea was to use this as part of a CRIU based snapshot, kexec to new
> system, restore.  However, why can't you do a local snapshot, restart
> qemu, restore using the PKRAM capsule to achieve exactly the same as
> MADV_DOEXEC does but using a system that's easy to reason about?  It
> may be slightly slower, but I think we're still talking milliseconds.


I've had another idea (that is probably impossible...).
What about a 'reverse mmap' operation.
Something that creates an fd whose contents are a chunk of the
processes address space.

	David

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