linux-kernel - Re: [PATCH v2 0/7] KVM: nVMX: Fixes for nested state migration when eVMCS is in use

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Message-ID: <8a8be89e-83e4-f9e8-698f-85a7cff76e8d@redhat.com>
Date:   Mon, 24 May 2021 16:01:00 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...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 v2 0/7] KVM: nVMX: Fixes for nested state migration when
 eVMCS is in use

On 17/05/21 15:50, Vitaly Kuznetsov wrote:
> Changes since v1 (Sean):
> - Drop now-unneeded curly braces in nested_sync_vmcs12_to_shadow().
> - Pass 'evmcs->hv_clean_fields' instead of 'bool from_vmentry' to
>    copy_enlightened_to_vmcs12().
> 
> Commit f5c7e8425f18 ("KVM: nVMX: Always make an attempt to map eVMCS after
> migration") fixed the most obvious reason why Hyper-V on KVM (e.g. Win10
>   + WSL2) was crashing immediately after migration. It was also reported
> that we have more issues to fix as, while the failure rate was lowered
> signifincatly, it was still possible to observe crashes after several
> dozens of migration. Turns out, the issue arises when we manage to issue
> KVM_GET_NESTED_STATE right after L2->L2 VMEXIT but before L1 gets a chance
> to run. This state is tracked with 'need_vmcs12_to_shadow_sync' flag but
> the flag itself is not part of saved nested state. A few other less
> significant issues are fixed along the way.
> 
> While there's no proof this series fixes all eVMCS related problems,
> Win10+WSL2 was able to survive 3333 (thanks, Max!) migrations without
> crashing in testing.
> 
> Patches are based on the current kvm/next tree.
> 
> Vitaly Kuznetsov (7):
>    KVM: nVMX: Introduce nested_evmcs_is_used()
>    KVM: nVMX: Release enlightened VMCS on VMCLEAR
>    KVM: nVMX: Ignore 'hv_clean_fields' data when eVMCS data is copied in
>      vmx_get_nested_state()
>    KVM: nVMX: Force enlightened VMCS sync from nested_vmx_failValid()
>    KVM: nVMX: Reset eVMCS clean fields data from prepare_vmcs02()
>    KVM: nVMX: Request to sync eVMCS from VMCS12 after migration
>    KVM: selftests: evmcs_test: Test that KVM_STATE_NESTED_EVMCS is never
>      lost
> 
>   arch/x86/kvm/vmx/nested.c                     | 110 ++++++++++++------
>   .../testing/selftests/kvm/x86_64/evmcs_test.c |  64 +++++-----
>   2 files changed, 115 insertions(+), 59 deletions(-)
> 

Looks good, I'm possibly expecting a v3 depending on what you think 
about my patch 1 suggestion.

Paolo