From: Xiaoyao Li <xiaoyao.li@intel.com>
To: Sean Christopherson <seanjc@google.com>,
Chenyi Qiang <chenyi.qiang@intel.com>
Cc: 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: Tue, 7 Sep 2021 21:45:12 +0800 [thread overview]
Message-ID: <118cd1b9-1b50-3173-05b8-4293412ca78c@intel.com> (raw)
In-Reply-To: <YTD9kIIzAz34Ieeu@google.com>
On 9/3/2021 12:36 AM, Sean Christopherson wrote:
> On Thu, Sep 02, 2021, Sean Christopherson wrote:
>> On Tue, Aug 03, 2021, Xiaoyao Li wrote:
>>> On 8/2/2021 11:46 PM, Sean Christopherson wrote:
>>>>>>> @@ -5642,6 +5653,31 @@ static int handle_bus_lock_vmexit(struct kvm_vcpu *vcpu)
>>>>>>> return 0;
>>>>>>> }
>>>>>>> +static int handle_notify(struct kvm_vcpu *vcpu)
>>>>>>> +{
>>>>>>> + unsigned long exit_qual = vmx_get_exit_qual(vcpu);
>>>>>>> +
>>>>>>> + if (!(exit_qual & NOTIFY_VM_CONTEXT_INVALID)) {
>>>>>>
>>>>>> What does CONTEXT_INVALID mean? The ISE doesn't provide any information whatsoever.
>>>>>
>>>>> It means whether the VM context is corrupted and not valid in the VMCS.
>>>>
>>>> Well that's a bit terrifying. Under what conditions can the VM context become
>>>> corrupted? E.g. if the context can be corrupted by an inopportune NOTIFY exit,
>>>> then KVM needs to be ultra conservative as a false positive could be fatal to a
>>>> guest.
>>>>
>>>
>>> Short answer is no case will set the VM_CONTEXT_INVALID bit.
>>
>> But something must set it, otherwise it wouldn't exist.
For existing Intel silicon, no case will set it. Maybe in the future new
case will set it.
> The condition(s) under
>> which it can be set matters because it affects how KVM should respond. E.g. if
>> the guest can trigger VM_CONTEXT_INVALID at will, then we should probably treat
>> it as a shutdown and reset the VMCS.
>
> Oh, and "shutdown" would be relative to the VMCS, i.e. if L2 triggers a NOTIFY
> exit with VM_CONTEXT_INVALID then KVM shouldn't kill the entire VM. The least
> awful option would probably be to synthesize a shutdown VM-Exit to L1. That
> won't communicate to L1 that vmcs12 state is stale/bogus, but I don't see any way
> to handle that via an existing VM-Exit reason :-/
>
>> But if VM_CONTEXT_INVALID can occur if and only if there's a hardware/ucode
>> issue, then we can do:
>>
>> if (KVM_BUG_ON(exit_qual & NOTIFY_VM_CONTEXT_INVALID, vcpu->kvm))
>> return -EIO;
>>
>> Either way, to enable this by default we need some form of documentation that
>> describes what conditions lead to VM_CONTEXT_INVALID.
I still don't know why the conditions lead to it matters. I think the
consensus is that once VM_CONTEXT_INVALID happens, the vcpu can no
longer run. Either KVM_BUG_ON() or a specific EXIT to userspace should
be OK?
next prev parent reply other threads:[~2021-09-07 13:45 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 [this message]
2021-09-09 18:59 ` Sean Christopherson
2021-09-13 2:58 ` Xiaoyao Li
2021-10-15 18:29 ` Sean Christopherson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=118cd1b9-1b50-3173-05b8-4293412ca78c@intel.com \
--to=xiaoyao.li@intel.com \
--cc=bp@alien8.de \
--cc=chenyi.qiang@intel.com \
--cc=hpa@zytor.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.com \
--cc=tglx@linutronix.de \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).