linux-kernel - Re: [PATCH 0/4] KVM: nVMX: Fix migration of nested guests when eVMCS is in use

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Message-ID: <87pmy7yfve.fsf@vitty.brq.redhat.com>
Date:   Mon, 03 May 2021 17:52:05 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] KVM: nVMX: Fix migration of nested guests when
 eVMCS is in use

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 03/05/21 17:08, Vitaly Kuznetsov wrote:
>> Win10 guests with WSL2 enabled sometimes crash on migration when
>> enlightened VMCS was used. The condition seems to be induced by the
>> situation when L2->L1 exit is caused immediately after migration and
>> before L2 gets a chance to run (e.g. when there's an interrupt pending).
>
> Interesting, I think it gets to nested_vmx_vmexit before
>
>                  if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
>                          if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
>                                  r = 0;
>                                  goto out;
>                          }
>                  }
>
> due to the infamous calls to check_nested_events that are scattered
> through KVM?

Yea,

vcpu_run() -> kvm_vcpu_running() -> vmx_check_nested_events() if I
remember it correctly.

-- 
Vitaly