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Date:   Tue, 13 Feb 2018 09:54:29 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Mark D Rustad <mrustad@gmail.com>
Cc:     Adam Borowski <kilobyte@angband.pl>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Andy Lutomirski <luto@kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Brian Gerst <brgerst@gmail.com>,
        David Laight <David.Laight@aculab.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Eduardo Valentin <eduval@amazon.com>,
        Will Deacon <will.deacon@arm.com>,
        "Liguori, Anthony" <aliguori@amazon.com>,
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        Hugh Dickins <hughd@google.com>,
        Kees Cook <keescook@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 00/31 v2] PTI support for x86_32
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On Sun, Feb 11, 2018 at 09:40:41AM -0800, Mark D Rustad wrote:
> > On Feb 11, 2018, at 2:59 AM, Adam Borowski <kilobyte@angband.pl> wrote:
> > 
> >> Does Debian make it easy to upgrade to a 64-bit kernel if you have a
> >> 32-bit install?
> > 
> > Quite easy, yeah.  Crossgrading userspace is not for the faint of the heart,
> > but changing just the kernel is fine.
> 
> ISTR that iscsi doesn't work when running a 64-bit kernel with a
> 32-bit userspace. I remember someone offered kernel patches to fix it,
> but I think they were rejected. I haven't messed with that stuff in
> many years, so perhaps the userspace side now has accommodation for
> it. It might be something to check on.

IPSEC doesn't work with a 64bit kernel and 32bit userspace right now.

Back in 2015 someone started to work on that, and properly marked that
the kernel could not handle this with commit 74005991b78a ("xfrm: Do not
parse 32bits compiled xfrm netlink msg on 64bits host")

This is starting to be hit by some Android systems that are moving
(yeah, slowly) to 4.4 :(

thanks,

greg k-h