KVM: nVMX: Don't evaluate "emulation required" on nested VM-Exit

Use the "internal" variants of setting segment registers when stuffing
state on nested VM-Exit in order to skip the "emulation required"
updates.  VM-Exit must always go to protected mode, and all segments are
mostly hardcoded (to valid values) on VM-Exit.  The bits of the segments
that aren't hardcoded are explicitly checked during VM-Enter, e.g. the
selector RPLs must all be zero.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-30-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -4267,7 +4267,7 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
 		seg.l = 1;
 	else
 		seg.db = 1;
-	vmx_set_segment(vcpu, &seg, VCPU_SREG_CS);
+	__vmx_set_segment(vcpu, &seg, VCPU_SREG_CS);
 	seg = (struct kvm_segment) {
 		.base = 0,
 		.limit = 0xFFFFFFFF,
@@ -4278,17 +4278,17 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
 		.g = 1
 	};
 	seg.selector = vmcs12->host_ds_selector;
-	vmx_set_segment(vcpu, &seg, VCPU_SREG_DS);
+	__vmx_set_segment(vcpu, &seg, VCPU_SREG_DS);
 	seg.selector = vmcs12->host_es_selector;
-	vmx_set_segment(vcpu, &seg, VCPU_SREG_ES);
+	__vmx_set_segment(vcpu, &seg, VCPU_SREG_ES);
 	seg.selector = vmcs12->host_ss_selector;
-	vmx_set_segment(vcpu, &seg, VCPU_SREG_SS);
+	__vmx_set_segment(vcpu, &seg, VCPU_SREG_SS);
 	seg.selector = vmcs12->host_fs_selector;
 	seg.base = vmcs12->host_fs_base;
-	vmx_set_segment(vcpu, &seg, VCPU_SREG_FS);
+	__vmx_set_segment(vcpu, &seg, VCPU_SREG_FS);
 	seg.selector = vmcs12->host_gs_selector;
 	seg.base = vmcs12->host_gs_base;
-	vmx_set_segment(vcpu, &seg, VCPU_SREG_GS);
+	__vmx_set_segment(vcpu, &seg, VCPU_SREG_GS);
 	seg = (struct kvm_segment) {
 		.base = vmcs12->host_tr_base,
 		.limit = 0x67,
@@ -4296,11 +4296,11 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
 		.type = 11,
 		.present = 1
 	};
-	vmx_set_segment(vcpu, &seg, VCPU_SREG_TR);
+	__vmx_set_segment(vcpu, &seg, VCPU_SREG_TR);
 
 	memset(&seg, 0, sizeof(seg));
 	seg.unusable = 1;
-	vmx_set_segment(vcpu, &seg, VCPU_SREG_LDTR);
+	__vmx_set_segment(vcpu, &seg, VCPU_SREG_LDTR);
 
 	kvm_set_dr(vcpu, 7, 0x400);
 	vmcs_write64(GUEST_IA32_DEBUGCTL, 0);

arch/x86/kvm/vmx/vmx.c

@@ -2719,8 +2719,6 @@ static __init int alloc_kvm_area(void)
 	return 0;
 }
 
-static void __vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
-
 static void fix_pmode_seg(struct kvm_vcpu *vcpu, int seg,
 		struct kvm_segment *save)
 {
@@ -3293,7 +3291,7 @@ static u32 vmx_segment_access_rights(struct kvm_segment *var)
 	return ar;
 }
 
-static void __vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
+void __vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	const struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];
@@ -3330,7 +3328,7 @@ static void __vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, in
 	vmcs_write32(sf->ar_bytes, vmx_segment_access_rights(var));
 }
 
-void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
+static void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg)
 {
 	__vmx_set_segment(vcpu, var, seg);
 

arch/x86/kvm/vmx/vmx.h

@@ -371,7 +371,7 @@ void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 void set_cr4_guest_host_mask(struct vcpu_vmx *vmx);
 void ept_save_pdptrs(struct kvm_vcpu *vcpu);
 void vmx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
-void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
+void __vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
 u64 construct_eptp(struct kvm_vcpu *vcpu, hpa_t root_hpa, int root_level);
 
 bool vmx_guest_inject_ac(struct kvm_vcpu *vcpu);