From: Paolo Bonzini <pbonzini@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Sean Christopherson <sean.j.christopherson@intel.com>
Cc: syzbot <syzbot+00be5da1d75f1cc95f6b@syzkaller.appspotmail.com>,
bp@alien8.de, hpa@zytor.com, jmattson@google.com,
joro@8bytes.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, mingo@redhat.com,
rkrcmar@redhat.com, syzkaller-bugs@googlegroups.com,
vkuznets@redhat.com, wanpengli@tencent.com, x86@kernel.org
Subject: Re: WARNING in vcpu_enter_guest
Date: Fri, 20 Mar 2020 11:33:22 +0100 [thread overview]
Message-ID: <6686bde5-c1e8-5be5-f27a-61403c419a91@redhat.com> (raw)
In-Reply-To: <87k13f516q.fsf@nanos.tec.linutronix.de>
On 20/03/20 01:18, Thomas Gleixner wrote:
>> No, it is possible to do that depending on the clock setup on the live
>> migration source. You could cause the warning anyway by setting the
>> clock to a very high (signed) value so that kernel_ns + kvmclock_offset
>> overflows.
>
> If that overflow happens, then the original and the new host have an
> uptime difference in the range of >200 hundreds of years. Very realistic
> scenario...
>
> Of course this can happen if you feed crap into the interface, but do
> you really think that forwarding all crap to a guest is the right thing
> to do?
>
> As we all know the hypervisor orchestration stuff is perfect and would
> never feed crap into the kernel which happily proliferates that crap to
> the guest...
But the point is, is there a sensible way to detect it? Only allowing
>= -2^62 and < 2^62 or something like that is an ad hoc fix for a
warning that probably will never trigger outside fuzzing. I would
expect that passing the wrong sign is a more likely mistake than being
off by 2^63.
This data is available everywhere between strace, kernel tracepoints and
QEMU tracepoints or guest checkpoint (live migration) data. I just
don't see much advantage in keeping the warning.
Paolo
next prev parent reply other threads:[~2020-03-20 10:33 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-29 8:20 WARNING in vcpu_enter_guest syzbot
2020-03-19 10:35 ` syzbot
2020-03-19 14:49 ` Sean Christopherson
2020-03-19 15:14 ` Paolo Bonzini
2020-03-19 17:35 ` Sean Christopherson
2020-03-19 17:39 ` Sean Christopherson
2020-03-19 17:44 ` Paolo Bonzini
2020-03-20 0:18 ` Thomas Gleixner
2020-03-20 10:33 ` Paolo Bonzini [this message]
2020-03-20 13:33 ` Thomas Gleixner
2020-03-22 3:31 ` syzbot
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