On Mon, Jun 8, 2020 at 12:19 PM Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > 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.christopherson@xxxxxxxxx > > Fixes: 644d711aa0e1 ("KVM: nVMX: Deciding if L0 or L1 should handle an L2 exit") > Cc: Jim Mattson <jmattson@xxxxxxxxxx> > Cc: Xiaoyao Li <xiaoyao.li@xxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Cc: Oliver Upton <oupton@xxxxxxxxxx> > Cc: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx> > Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx> > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> Reviewed-by: Oliver Upton <oupton@xxxxxxxxxx> > --- > > 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 >
