linux-kernel - Re: [PATCH v3 00/11] KVM: nVMX: Fixes for nested state migration when eVMCS is in use

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Message-ID: <87mtrxyer2.fsf@vitty.brq.redhat.com>
Date:   Thu, 10 Jun 2021 16:29:37 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 00/11] KVM: nVMX: Fixes for nested state migration
 when eVMCS is in use

Vitaly Kuznetsov <vkuznets@...hat.com> writes:

> Changes since v2:
> - 'KVM: nVMX: Use '-1' in 'hv_evmcs_vmptr' to indicate that eVMCS is not in
>  use'/ 'KVM: nVMX: Introduce 'EVMPTR_MAP_PENDING' post-migration state'
>  patches instead of 'KVM: nVMX: Introduce nested_evmcs_is_used()' [Paolo]
> - 'KVM: nVMX: Don't set 'dirty_vmcs12' flag on enlightened VMPTRLD' patch
>  added [Max]
> - 'KVM: nVMX: Release eVMCS when enlightened VMENTRY was disabled' patch
>   added.
> - 'KVM: nVMX: Make copy_vmcs12_to_enlightened()/copy_enlightened_to_vmcs12()
>  return 'void'' patch added [Paolo]
> - R-b tags added [Max]
>
> Original description:
>
> 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.

Paolo, Max,

Just to double-check: are we good here? I know there are more
improvements/ideas to explore but I'd like to treat this patchset as a
set of fixes, it would be unfortunate if we miss 5.14.

-- 
Vitaly