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: <31df7026-9500-a802-b23c-4f2233f120d5@redhat.com>
Date:   Thu, 10 Jun 2021 17:31:45 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...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

On 10/06/21 16:29, Vitaly Kuznetsov wrote:
> 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.
> 

Yes, I was busy the last couple of weeks but I am back now.

Paolo