linux-kernel - Re: 4.15-rc6+ hang

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Message-ID: <1e1b4534-b0b4-90c9-479b-29058047f1e9@oracle.com>
Date:   Thu, 4 Jan 2018 21:02:17 -0700
From:   Tom Hromatka <tom.hromatka@...cle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dhaval Giani <dhaval.giani@...cle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 4.15-rc6+ hang



On 01/04/2018 07:22 PM, Linus Torvalds wrote:
> On Thu, Jan 4, 2018 at 5:36 PM, Tom Hromatka <tom.hromatka@...cle.com> wrote:
>> I am seeing a hang running kernel 4.15-rc6+ on a vanilla VirtualBox VM.
>> (VirtualBox version 5.0.40)
> Any chance of bisecting this?
>
> I could imagine that all the stuff we now do for page table isolation
> might confuse the VM.

Yes, I can try and bisect this.

>> When I boot this kernel, it hangs and falls back into dracut. Here's
>> the boot log immediately prior to the hang:
> So a few questions:
>
>   (a) does it work with "pti=no" on the kernel command line

pti=no also hung in the same fashion with the 4.15-rc6+
kernel.

>
>   (b) what was the last kernel that worked? Is 4.15-rc5 fine, for example?

4.15-rc5 hung as well.  I'll go further back and see what I
can find.

>> [    0.000000] ------------[ cut here ]------------
>> [    0.000000] XSAVE consistency problem, dumping leaves
> I think this is a vbox issue, with virtualbox not exposing all the
> xsave state, so that when the kernel adds up the xsave areas, the end
> result doesn't match what the total size is reported to be.

It seems probable that this is a VirtualBox issue.  I was
able to boot my exact 4.15-rc6+ kernel in qemu-kvm v1.5.3
just fine.

>
> I suspect you _should_ have gotten that before too, independently of the hang.

4.15-rc5 also exhibits the xsave issue in VirtualBox.

Thanks.

Tom

>
>                    Linus