linux-kernel - Re: [syzbot] general protection fault in try_grab_compound

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Message-ID: <YOy0HAnhsXJ4W210@google.com>
Date:   Mon, 12 Jul 2021 21:29:00 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     syzbot <syzbot+a3fcd59df1b372066f5a@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, bp@...en8.de, hpa@...or.com,
        jmattson@...gle.com, joro@...tes.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mark.rutland@....com, masahiroy@...nel.org, mingo@...hat.com,
        pbonzini@...hat.com, peterz@...radead.org,
        rafael.j.wysocki@...el.com, rostedt@...dmis.org,
        sedat.dilek@...il.com, syzkaller-bugs@...glegroups.com,
        vitor@...saru.org, vkuznets@...hat.com, wanpengli@...cent.com,
        will@...nel.org, x86@...nel.org
Subject: Re: [syzbot] general protection fault in try_grab_compound_head

On Thu, Jul 08, 2021, Thomas Gleixner wrote:
> On Sat, Jul 03 2021 at 13:24, syzbot wrote:
> > syzbot has bisected this issue to:
> >
> > commit 997acaf6b4b59c6a9c259740312a69ea549cc684
> > Author: Mark Rutland <mark.rutland@....com>
> > Date:   Mon Jan 11 15:37:07 2021 +0000
> >
> >     lockdep: report broken irq restoration
> 
> That's the commit which makes the underlying problem visible:
> 
>        raw_local_irq_restore() called with IRQs enabled
> 
> and is triggered by this call chain:
> 
>  kvm_wait arch/x86/kernel/kvm.c:860 [inline]
>  kvm_wait+0xc3/0xe0 arch/x86/kernel/kvm.c:837

And the bug in kvm_wait() was fixed by commit f4e61f0c9add ("x86/kvm: Fix broken
irq restoration in kvm_wait").  The bisection is bad, syzbot happened into the
kvm_wait() WARN and got distracted.  The original #GP looks stable, if someone
from mm land has bandwidth.