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    Subject[PATCH 4.9 039/128] KVM: nVMX: Consult only the "basic" exit reason when routing nested exit
    Date
    From: Sean Christopherson <sean.j.christopherson@intel.com>

    commit 2ebac8bb3c2d35f5135466490fc8eeaf3f3e2d37 upstream.

    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 statement in nested_vmx_exit_reflected()
    currently defaults to "true", i.e. reflects 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).

    Fixes: 644d711aa0e1 ("KVM: nVMX: Deciding if L0 or L1 should handle an L2 exit")
    Cc: Jim Mattson <jmattson@google.com>
    Cc: Xiaoyao Li <xiaoyao.li@intel.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    Message-Id: <20200227174430.26371-1-sean.j.christopherson@intel.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/kvm/vmx.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/x86/kvm/vmx.c
    +++ b/arch/x86/kvm/vmx.c
    @@ -8207,7 +8207,7 @@ static bool nested_vmx_exit_handled(stru
    return true;
    }

    - switch (exit_reason) {
    + switch ((u16)exit_reason) {
    case EXIT_REASON_EXCEPTION_NMI:
    if (is_nmi(intr_info))
    return false;

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