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

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Message-ID: <389f79f9-f1a5-963e-dd05-4d0aaabb5346@oracle.com>
Date:   Fri, 31 Jul 2020 15:41:37 -0400
From:   Steven Sistare <steven.sistare@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org
Cc:     mhocko@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org, arnd@...db.de,
        ebiederm@...ssion.com, keescook@...omium.org, gerg@...ux-m68k.org,
        ktkhai@...tuozzo.com, christian.brauner@...ntu.com,
        peterz@...radead.org, esyr@...hat.com, jgg@...pe.ca,
        christian@...lner.me, areber@...hat.com, cyphar@...har.com
Subject: Re: [RFC PATCH 0/5] madvise MADV_DOEXEC

On 7/27/2020 1:11 PM, 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 forgot to mention, our use case is not just theoretical.  It has been implemented
and is pretty cool (but I am biased).  The pause time for the guest is in the
100 - 200 msec range.  We submitted qemu patches for review based on the MADV_DOEXEC
proposal.  In case you are curious:
  https://lore.kernel.org/qemu-devel/1596122076-341293-1-git-send-email-steven.sistare@oracle.com/

- Steve