linux-kernel - Re: [PATCH stable-4.19 1/2] KVM: nVMX: do not use dangling shadow VMCS after guest reset

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Date:   Mon, 29 Jul 2019 11:29:16 +0200
From:   Jack Wang <jack.wang.usish@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>, stable@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH stable-4.19 1/2] KVM: nVMX: do not use dangling shadow
 VMCS after guest reset

Paolo Bonzini <pbonzini@...hat.com> 于2019年7月29日周一 上午11:10写道：
>
> On 29/07/19 10:58, Jack Wang wrote:
> > Vitaly Kuznetsov <vkuznets@...hat.com> 于2019年7月25日周四 下午3:29写道：
> >>
> >> From: Paolo Bonzini <pbonzini@...hat.com>
> >>
> >> [ Upstream commit 88dddc11a8d6b09201b4db9d255b3394d9bc9e57 ]
> >>
> >> If a KVM guest is reset while running a nested guest, free_nested will
> >> disable the shadow VMCS execution control in the vmcs01.  However,
> >> on the next KVM_RUN vmx_vcpu_run would nevertheless try to sync
> >> the VMCS12 to the shadow VMCS which has since been freed.
> >>
> >> This causes a vmptrld of a NULL pointer on my machime, but Jan reports
> >> the host to hang altogether.  Let's see how much this trivial patch fixes.
> >>
> >> Reported-by: Jan Kiszka <jan.kiszka@...mens.com>
> >> Cc: Liran Alon <liran.alon@...cle.com>
> >> Cc: stable@...r.kernel.org
> >> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> >
> > Hi all,
> >
> > Do we need to backport the fix also to stable 4.14?  It applies
> > cleanly and compiles fine.
>
> The reproducer required newer kernels that support KVM_GET_NESTED_STATE
> and KVM_SET_NESTED_STATE, so it would be hard to test it.  However, the
> patch itself should be safe.
>
> Paolo

Thanks Paolo for confirmation. I'm asking because we had one incident
in our production with 4.14.129 kernel,
System is Skylake Gold cpu, first kvm errors, host hung afterwards

kernel: [1186161.091160] kvm: vmptrld           (null)/6bfc00000000 failed
kernel: [1186161.091537] kvm: vmclear fail:           (null)/6bfc00000000
kernel: [1186186.490300] watchdog: BUG: soft lockup - CPU#54 stuck for
23s! [qemu:16639]

Hi Sasha, hi Greg,

Would be great if you can pick this patch also to 4.14 kernel.

Best regards,
Jack Wang