Consult only the basic exit reason, i.e. bits 15:0 of vmcs.EXIT_REASON, when determining whether a nested VM-Exit should be reflected into L1 or handled by KVM in L0.
For better or worse, the switch statements nested_vmx_l0_wants_exit() and nested_vmx_l1_wants_exit() default to reflecting the VM-Exit into L1 for any nested VM-Exit without dedicated logic. Because the case statements only contain the basic exit reason, any VM-Exit with modifier bits set will be reflected to L1, even if KVM intended to handle it in L0. Practically speaking, this only affects EXIT_REASON_MCE_DURING_VMENTRY, i.e. a #MC that occurs on nested VM-Enter would be incorrectly routed to L1, as "failed VM-Entry" is the only modifier that KVM can currently encounter. The SMM modifiers will never be generated as KVM doesn't support/employ a SMI Transfer Monitor. Ditto for "exit from enclave", as KVM doesn't yet support virtualizing SGX, i.e. it's impossible to enter an enclave in a KVM guest (L1 or L2). Note, the original version of this fix[*] is functionally equivalent and far more suited to backporting as the affected code was refactored since the original patch was posted. [*] https://lkml.kernel.org/r/20200227174430.26371-1-sean.j.christopher...@intel.com Fixes: 644d711aa0e1 ("KVM: nVMX: Deciding if L0 or L1 should handle an L2 exit") Cc: Jim Mattson <jmatt...@google.com> Cc: Xiaoyao Li <xiaoyao...@intel.com> Cc: sta...@vger.kernel.org Cc: Oliver Upton <oup...@google.com> Cc: Krish Sadhukhan <krish.sadhuk...@oracle.com> Cc: Miaohe Lin <linmia...@huawei.com> Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com> --- Another wounded soldier. Oliver, Krish, and Miaohe all provided reviews for v1, but I didn't feel comfortable adding the tags to v2 because this is far from a straight rebase. v2: Rebased to kvm/queue, commit fb7333dfd812 ("KVM: SVM: fix calls ..."). arch/x86/kvm/vmx/nested.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index bcb50724be38..adb11b504d5c 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -5672,7 +5672,7 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu, u32 exit_reason) { u32 intr_info; - switch (exit_reason) { + switch ((u16)exit_reason) { case EXIT_REASON_EXCEPTION_NMI: intr_info = vmx_get_intr_info(vcpu); if (is_nmi(intr_info)) @@ -5733,7 +5733,7 @@ static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu, u32 exit_reason) struct vmcs12 *vmcs12 = get_vmcs12(vcpu); u32 intr_info; - switch (exit_reason) { + switch ((u16)exit_reason) { case EXIT_REASON_EXCEPTION_NMI: intr_info = vmx_get_intr_info(vcpu); if (is_nmi(intr_info)) -- 2.26.0
