KVM: SEV: Move SEV's GP_VECTOR intercept setup to SEV

Currently SVM setup is done sequentially in
init_vmcb() -> sev_init_vmcb() -> sev_es_init_vmcb() and tries
keeping SVM/SEV/SEV-ES bits separated. One of the exceptions
is #GP intercept which init_vmcb() skips setting for SEV guests and
then sev_es_init_vmcb() needlessly clears it.

Remove the SEV check from init_vmcb(). Clear the #GP intercept in
sev_init_vmcb(). SEV-ES will use the SEV setting.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Alexey Kardashevskiy <aik@amd.com>
Reviewed-by: Carlos Bilbao <carlos.bilbao@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Santosh Shukla <santosh.shukla@amd.com>
Link: https://lore.kernel.org/r/20230615063757.3039121-3-aik@amd.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 07756b7348ae..fd6e316c1a23 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2974,9 +2974,6 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
 	svm_set_intercept(svm, TRAP_CR4_WRITE);
 	svm_set_intercept(svm, TRAP_CR8_WRITE);
 
-	/* No support for enable_vmware_backdoor */
-	clr_exception_intercept(svm, GP_VECTOR);
-
 	/* Can't intercept XSETBV, HV can't modify XCR0 directly */
 	svm_clr_intercept(svm, INTERCEPT_XSETBV);
 
@@ -3002,6 +2999,12 @@ void sev_init_vmcb(struct vcpu_svm *svm)
 	svm->vmcb->control.nested_ctl |= SVM_NESTED_CTL_SEV_ENABLE;
 	clr_exception_intercept(svm, UD_VECTOR);
 
+	/*
+	 * Don't intercept #GP for SEV guests, e.g. for the VMware backdoor, as
+	 * KVM can't decrypt guest memory to decode the faulting instruction.
+	 */
+	clr_exception_intercept(svm, GP_VECTOR);
+
 	if (sev_es_guest(svm->vcpu.kvm))
 		sev_es_init_vmcb(svm);
 }