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From: Sean Christopherson <seanjc@google.com>
To: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Chenyi Qiang <chenyi.qiang@intel.com>,
	pbonzini@redhat.com, vkuznets@redhat.com, wanpengli@tencent.com,
	jmattson@google.com, joro@8bytes.org, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] KVM: VMX: Enable Notify VM exit
Date: Fri, 15 Oct 2021 18:29:07 +0000	[thread overview]
Message-ID: <YWnIc7wVLBjaTcBX@google.com> (raw)
In-Reply-To: <b6f2acf8-eef4-9483-1937-191209bcef9f@intel.com>

On Mon, Sep 13, 2021, Xiaoyao Li wrote:
> On 9/10/2021 2:59 AM, Sean Christopherson wrote:
> > Yes, and no longer being able to run the vCPU is precisely the problem.  The
> > condition(s) matters because if there's a possibility, however small, that enabling
> > NOTIFY_WINDOW can kill a well-behaved guest then it absolutely cannot be enabled by
> > default.
> 
> For now, no condition will set it. For future, I believe it will be set only
> for some fatal case. However, we cannot guarantee no silicon bug to break a
> well-behaved the guest. Maybe let's make it opt-in?

Ya, I think an off-by-default module param makes sense.

> > > Either KVM_BUG_ON() or a specific EXIT to userspace should be OK?
> > 
> > Not if the VM_CONTEXT_INVALID happens while L2 is running.  If software can trigger
> > VM_CONTEXT_INVALID at will, then killing the VM would open up the door to a
> > malicious L2 killing L1 (which would be rather ironic since this is an anti-DoS
> > feature).  IIUC, VM_CONTEXT_INVALID only means the current VMCS is garbage, thus
> > an occurence while L2 is active means that vmcs02 is junk, but L1's state in vmcs01,
> > vmcs12, etc... is still valid.
> > 
> 
> Maybe we can kill the L2 when VM_CONTEXT_INVALID happens in L2.

Ya, synthesizing a nested EXIT_REASON_TRIPLE_FAULT and sanitizing vmcs02/vmcs12 is
the least awful solution I can think of.  I could have sworn I suggested as much,
but apparently that thought never made it from my brain to the keyboard.

      reply	other threads:[~2021-10-15 18:29 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-25  5:12 [PATCH v2] KVM: VMX: Enable Notify VM exit Tao Xu
2021-06-02 10:31 ` Vitaly Kuznetsov
2021-06-03  1:23   ` Tao Xu
2021-06-03 13:43     ` Vitaly Kuznetsov
2021-06-03  1:25   ` Xiaoyao Li
2021-06-03 13:35     ` Jim Mattson
2021-06-07  9:24       ` Xiaoyao Li
2021-06-03 13:52     ` Vitaly Kuznetsov
2021-06-07  9:23       ` Xiaoyao Li
2021-06-24  4:52 ` Tao Xu
2021-07-22  3:25 ` Xiaoyao Li
2021-07-30 20:41 ` Sean Christopherson
2021-08-02 12:53   ` Xiaoyao Li
2021-08-02 15:46     ` Sean Christopherson
2021-08-03  0:38       ` Xiaoyao Li
2021-09-02  9:28         ` Chenyi Qiang
2021-09-02 16:29           ` Sean Christopherson
2021-09-07 13:33             ` Xiaoyao Li
2021-09-09 18:47               ` Sean Christopherson
2021-09-10  7:39                 ` Xiaoyao Li
2021-09-10 17:55                   ` Sean Christopherson
2021-09-02 16:15         ` Sean Christopherson
2021-09-02 16:36           ` Sean Christopherson
2021-09-07 13:45             ` Xiaoyao Li
2021-09-09 18:59               ` Sean Christopherson
2021-09-13  2:58                 ` Xiaoyao Li
2021-10-15 18:29                   ` Sean Christopherson [this message]

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