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

[Paolo Bonzini]

On 10/06/21 16:29, Vitaly Kuznetsov wrote:
> Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> 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