[PATCH 0/2] KVM: x86: Reset MMU back to the root MMU when leaving guest mode

[Paolo Bonzini]

Fix a bug where KVM fails to unwind vcpu->arch.mmu back to the root MMU after
leaving guest mode on a failed entry to L2 via RSM or KVM_SET_NETSED_STATE.
If KVM also frees nested state before the next entry to L1 (or maybe even
after?), trying to construct the shadow root will hit a NULL pointer deref
when trying to get vmcs12->eptp.

The only known instance of the bug is in patch 1; Sean's patch 2 avoids
the moving the reset to the place where the vCPU goes back to L1 for both
nSVM and nVMX.  However, it conflicts with pre-7.3 code due to the separation
of kvm_mmu and kvm_pagewalk; and it will also conflict with the stable-worthy
v3 of https://lore.kernel.org/kvm/20261011001303.723721-1-mlevitsk@xxxxxxxxxx/,
so it will only be applied to kvm/next.

Thanks,

Paolo

Amirmohammad Eftekhar (1):
  KVM: nVMX: Reset MMU back to the root MMU if loading L2 state fails for !VM-Entry

Sean Christopherson (1):
  KVM: x86: Reset MMU back to the root MMU when leaving guest mode

 arch/x86/kvm/regs.h       | 2 ++
 arch/x86/kvm/svm/nested.c | 8 --------
 arch/x86/kvm/vmx/nested.c | 8 --------
 3 files changed, 2 insertions(+), 16 deletions(-)

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2.56.0