From: Sean Christopherson <sean.j.christopherson@intel.com>

Date: Thu, 27 Feb 2020 09:44:30 -0800

Subject: KVM: nVMX: Consult only the "basic" exit reason when routing nested

 exit

Git-commit: 2ebac8bb3c2d35f5135466490fc8eeaf3f3e2d37

Patch-mainline: v5.8-rc1

References: bsc#1188773

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: Jose R. Ziviani <jziviani@suse.de>

---

 arch/x86/kvm/vmx/nested.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c

index a20083ac1ea3..6ee196da166d 100644

--- a/arch/x86/kvm/vmx/nested.c

+++ b/arch/x86/kvm/vmx/nested.c

@@ -5380,7 +5380,7 @@ bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)

 				vmcs_read32(VM_EXIT_INTR_ERROR_CODE),

 				KVM_ISA_VMX);

-	switch (exit_reason) {

+	switch ((u16)exit_reason) {

 	case EXIT_REASON_EXCEPTION_NMI:

 		if (is_nmi(intr_info))

 			return false;

-- 

2.32.0