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Subject: Re: PROBLEM: Xen paging-request boot failure since 4.19.5
To:     Ken Pizzini <kkpp@explicate.org>,
        Thomas Gleixner <tglx@linutronix.de>
Cc:     linux-kernel@vger.kernel.org,
        xen-devel <xen-devel@lists.xenproject.org>
References: <20181219212537.GA25174@144vak35.msa.explicate.org>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Date:   Thu, 20 Dec 2018 11:12:40 -0500
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 12/19/18 4:25 PM, Ken Pizzini wrote:
> Since 4.19.5 I have not been able to boot kernels on my Xen-hosted VM on
> a system with an Intel Xeon L5520 processor (microcode 0x1d).
>
> 4.19.4 worked fine; I've tried kernels 4.19.5, 4.19.6, 4.19.7 4.19.9, 4.19.10,
> 4.20-rc7, and they all throw:
>      BUG: unable to handle kernel paging request at ffff88903fffc000
>      PGD 1c0c067 P4D 1c0c067 PUD 0
>      Oops: 0000 [#1] PREEMPT SMP NOPTI
>      ... [register dump and call trace omitted, since I believe I located the
>           offending source code]
>      Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
>      Kernel Offset: disabled
> early in the system boot (fine details might differ; I did not carefully
> record the result of each test).
>
> I finally had time to do some bisection, and the problem traces back to commit
>     d52888aa2753e3063a9d3a0c9f72f94aa9809c15
>     in tree fbbb33771ac6c392caeb283163a594f1a7e6d04d
> (x86/mm: Move LDT remap out of KASLR region on 5-level paging).
>
> After backing-out this one commit, I have successfully built and booted
> 4.19.5, 4.19.10 and 4.20-rc7 (I haven't bothered trying other versions).
> (The VM is currently running my patched 4.19.10 without any apparent problem.)
>
> Notes: all 4.19.* builds are of Gentoo's "gentoo-sources" tree (which include
> standard Gentoo patches), plus wireguard; the 4.20-rc7 build was unpatched.
> I have been successfully running a different build of each 4.19.* version
> on my laptop (with many more device drivers enabled), so the problem
> is unlikely to be due to the build toolchain (which is common to both
> of my build trees).
>
>
> Let me know if there is more information that you would find helpful,
> or if you have patches that you'd like me to test.
>
> 		--Ken Pizzini


This is addressed by https://lkml.org/lkml/2018/12/11/266 but has not
been merged yet.

(Next time for Xen issues please copy xen-devel@lists.xenproject.org)


-boris