The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 764643a6be07445308e492a528197044c801b3ba Mon Sep 17 00:00:00 2001 From: Sean Christopherson seanjc@google.com Date: Tue, 14 Jun 2022 21:58:28 +0000 Subject: [PATCH] KVM: nVMX: Snapshot pre-VM-Enter DEBUGCTL for !nested_run_pending case
If a nested run isn't pending, snapshot vmcs01.GUEST_IA32_DEBUGCTL irrespective of whether or not VM_ENTRY_LOAD_DEBUG_CONTROLS is set in vmcs12. When restoring nested state, e.g. after migration, without a nested run pending, prepare_vmcs02() will propagate nested.vmcs01_debugctl to vmcs02, i.e. will load garbage/zeros into vmcs02.GUEST_IA32_DEBUGCTL.
If userspace restores nested state before MSRs, then loading garbage is a non-issue as loading DEBUGCTL will also update vmcs02. But if usersepace restores MSRs first, then KVM is responsible for propagating L2's value, which is actually thrown into vmcs01, into vmcs02.
Restoring L2 MSRs into vmcs01, i.e. loading all MSRs before nested state is all kinds of bizarre and ideally would not be supported. Sadly, some VMMs do exactly that and rely on KVM to make things work.
Note, there's still a lurking SMM bug, as propagating vmcs01's DEBUGCTL to vmcs02 across RSM may corrupt L2's DEBUGCTL. But KVM's entire VMX+SMM emulation is flawed as SMI+RSM should not toouch _any_ VMCS when use the "default treatment of SMIs", i.e. when not using an SMI Transfer Monitor.
Link: https://lore.kernel.org/all/Yobt1XwOfb5M6Dfa@google.com Fixes: 8fcc4b5923af ("kvm: nVMX: Introduce KVM_CAP_NESTED_STATE") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20220614215831.3762138-3-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 66c25bb56938..4a53e0c73445 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -3379,7 +3379,8 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu, if (likely(!evaluate_pending_interrupts) && kvm_vcpu_apicv_active(vcpu)) evaluate_pending_interrupts |= vmx_has_apicv_interrupt(vcpu);
- if (!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) + if (!vmx->nested.nested_run_pending || + !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS)) vmx->nested.vmcs01_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL); if (kvm_mpx_supported() && (!vmx->nested.nested_run_pending ||