KVM: x86: Move vendor CR4 validity check to dedicated kvm_x86_ops hook

Split out VMX's checks on CR4.VMXE to a dedicated hook, .is_valid_cr4(),
and invoke the new hook from kvm_valid_cr4().  This fixes an issue where
KVM_SET_SREGS would return success while failing to actually set CR4.

Fixing the issue by explicitly checking kvm_x86_ops.set_cr4()'s return
in __set_sregs() is not a viable option as KVM has already stuffed a
variety of vCPU state.

Note, kvm_valid_cr4() and is_valid_cr4() have different return types and
inverted semantics.  This will be remedied in a future patch.

Fixes: 5e1746d6205d ("KVM: nVMX: Allow setting the VMXE bit in CR4")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20201007014417.29276-5-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 18 insertions, 13 deletions

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d9a4526c730c..3327964a1e2e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3095,7 +3095,23 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long pgd,
 		vmcs_writel(GUEST_CR3, guest_cr3);
 }
 
-int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+static bool vmx_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+{
+	/*
+	 * We operate under the default treatment of SMM, so VMX cannot be
+	 * enabled under SMM.  Note, whether or not VMXE is allowed at all is
+	 * handled by kvm_valid_cr4().
+	 */
+	if ((cr4 & X86_CR4_VMXE) && is_smm(vcpu))
+		return false;
+
+	if (to_vmx(vcpu)->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
+		return false;
+
+	return true;
+}
+
+void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	/*
@@ -3123,17 +3139,6 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 		}
 	}
 
-	/*
-	 * We operate under the default treatment of SMM, so VMX cannot be
-	 * enabled under SMM.  Note, whether or not VMXE is allowed at all is
-	 * handled by kvm_valid_cr4().
-	 */
-	if ((cr4 & X86_CR4_VMXE) && is_smm(vcpu))
-		return 1;
-
-	if (vmx->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
-		return 1;
-
 	vcpu->arch.cr4 = cr4;
 	kvm_register_mark_available(vcpu, VCPU_EXREG_CR4);
 
@@ -3164,7 +3169,6 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 
 	vmcs_writel(CR4_READ_SHADOW, cr4);
 	vmcs_writel(GUEST_CR4, hw_cr4);
-	return 0;
 }
 
 void vmx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
@@ -7612,6 +7616,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
 	.get_cpl = vmx_get_cpl,
 	.get_cs_db_l_bits = vmx_get_cs_db_l_bits,
 	.set_cr0 = vmx_set_cr0,
+	.is_valid_cr4 = vmx_is_valid_cr4,
 	.set_cr4 = vmx_set_cr4,
 	.set_efer = vmx_set_efer,
 	.get_idt = vmx_get_idt,