linux-kernel - Re: [PATCH v2 2/2] kexec_file: Increase maximum file size to 4G

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Message-ID: <Yp/tL5F7TFdwk8Sj@MiWiFi-R3L-srv>
Date:   Wed, 8 Jun 2022 08:28:31 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
Cc:     Sasha Levin <sashal@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, rburanyi@...gle.com,
        Greg Thelen <gthelen@...gle.com>, viro@...iv.linux.org.uk,
        kexec mailing list <kexec@...ts.infradead.org>,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] kexec_file: Increase maximum file size to 4G

On 06/07/22 at 12:02pm, Pasha Tatashin wrote:
> On Sun, Jun 5, 2022 at 10:56 PM Baoquan He <bhe@...hat.com> wrote:
> >
> > On 05/27/22 at 02:55am, Pasha Tatashin wrote:
> > > In some case initrd can be large. For example, it could be a netboot
> > > image loaded by u-root, that is kexec'ing into it.
> > >
> > > The maximum size of initrd is arbitrary set to 2G. Also, the limit is
> > > not very obvious because it is hidden behind a generic INT_MAX macro.
> > >
> > > Theoretically, we could make it LONG_MAX, but it is safer to keep it
> > > sane, and just increase it to 4G.
> >
> > Do we need to care about 32bit system where initramfs could be larger
> > than 2G? On 32bit system, SSIZE_MAX is still 2G, right?
> 
> Yes, on 32-bit SSIZE_MAX is still 2G, so we are safe to keep 32-bit
> systems run exactly as today.
> 
> #define KEXEC_FILE_SIZE_MAX    min_t(s64, 4LL << 30, SSIZE_MAX)
> Is meant to protect against running over the 2G limit on 32-bit systems.

OK. In fact I was wrong. I386 doesn't have kexec_file loading support.

> 
> >
> > Another concern is if 2G is enough. If we can foresee it might need be
                          ~~ 4G, typo
> > enlarged again in a near future, LONG_MAX certainly is not a good
> > value, but a little bigger multiple of 2G can be better?
> 
> This little series enables increasing the max value above 2G, but
> still keeps it within a sane size i.e. 4G, If 4G seems too small, I
> can change it to 8G or 16G instead of 4G.

Just raising to try to discuss if 4G is enough. I have no knowledge
about how much is enough, and we don't need to guess, if you think 4G is
enough according to information you get, that's OK. We can wait a while
to see if other people have words about the vlaue. If no, then 4G is a
good one.

Thanks
Baoquan