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

Vitaly Kuznetsov [off-list ref] writes:

quoted

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