linux-kernel - [PATCH 0/5] KVM: nVMX: Support loading MSRs before nested state

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Date:   Tue, 14 Jun 2022 21:58:26 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Lei Wang <lei4.wang@...el.com>
Subject: [PATCH 0/5] KVM: nVMX: Support loading MSRs before nested state

Fix two edge cases in nested VM-Enter where KVM loads garbage into
BNDCFGS and/or DEBUGCTL when migrating a vCPU with L2 active.  If userspace
restores MSRs before nested state, userspace expects KVM to propagate L2's
values to vmcs02.  KVM already mostly handles this scenario, so even though
I personally think it's rather ridiculous, it's easy for KVM to support,
and given that our VMM does KVM_SET_MSRS before KVM_SET_NESTED_STATE...

Patches 4 and 5 are minor optimizations to handle BNDCFGS more like
DEBUGCTL and/or the PKS MSR.

Sean Christopherson (5):
  KVM: nVMX: Snapshot pre-VM-Enter BNDCFGS for !nested_run_pending case
  KVM: nVMX: Snapshot pre-VM-Enter DEBUGCTL for !nested_run_pending case
  KVM: nVMX: Rename nested.vmcs01_* fields to nested.pre_vmenter_*
  KVM: nVMX: Save BNDCFGS to vmcs12 iff relevant controls are exposed to
    L1
  KVM: nVMX: Update vmcs12 on BNDCFGS write, not at vmcs02=>vmcs12 sync

 arch/x86/kvm/vmx/nested.c | 16 ++++++++--------
 arch/x86/kvm/vmx/vmx.c    | 13 +++++++++++++
 arch/x86/kvm/vmx/vmx.h    | 15 ++++++++++++---
 3 files changed, 33 insertions(+), 11 deletions(-)

base-commit: 8baacf67c76c560fed954ac972b63e6e59a6fba0
-- 
2.36.1.476.g0c4daa206d-goog