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Date:   Thu, 25 Feb 2021 12:25:11 -0800
From:   Sean Christopherson <seanjc@google.com>
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     Borislav Petkov <bp@alien8.de>,
        syzbot <syzbot+42a71c84ef04577f1aef@syzkaller.appspotmail.com>,
        Dave Hansen <dave.hansen@intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        KVM list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Lorenzo Stoakes <lstoakes@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vitaly Kuznetsov <vkuznets@redhat.com>, wanpengli@tencent.com,
        the arch/x86 maintainers <x86@kernel.org>,
        syzkaller <syzkaller@googlegroups.com>
Subject: Re: general protection fault in vmx_vcpu_run (2)
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On Thu, Feb 25, 2021, Dmitry Vyukov wrote:
> On Wed, Feb 24, 2021 at 7:08 PM 'Sean Christopherson' via
> syzkaller-bugs <syzkaller-bugs@googlegroups.com> wrote:
> >
> > On Wed, Feb 24, 2021, Borislav Petkov wrote:
> > > Hi Dmitry,
> > >
> > > On Wed, Feb 24, 2021 at 06:12:57PM +0100, Dmitry Vyukov wrote:
> > > > Looking at the bisection log, the bisection was distracted by something else.
> > >
> > > Meaning the bisection result:
> > >
> > > 167dcfc08b0b ("x86/mm: Increase pgt_buf size for 5-level page tables")
> > >
> > > is bogus?
> >
> > Ya, looks 100% bogus.
> >
> > > > You can always find the original reported issue over the dashboard link:
> > > > https://syzkaller.appspot.com/bug?extid=42a71c84ef04577f1aef
> > > > or on lore:
> > > > https://lore.kernel.org/lkml/0000000000007ff56205ba985b60@google.com/
> > >
> > > Ok, so this looks like this is trying to run kvm ioctls *in* a guest,
> > > i.e., nested. Right?
> >
> > Yep.  I tried to run the reproducer yesterday, but the kernel config wouldn't
> > boot my VM.  I haven't had time to dig in.  Anyways, I think you can safely
> > assume this is a KVM issue unless more data comes along that says otherwise.
> 
> Interesting. What happens? Does the kernel crash? Userspace crash?
> Rootfs is not mounted? Or something else?

Not sure, it ended up in the EFI shell instead of the kernel (running with QEMU's
-kernel).  My QEMU+KVM setup does a variety of shenanigans, I'm guessing it's an
incompatibility in my setup.